What Are Intellectual Disability and Developmental Disabilities?
A guide to intellectual disability, developmental disabilities, and IDD terminology and supports
Quick Answer
Intellectual disability refers to significant limitations in intellectual functioning and adaptive behavior that begin before the age of 22. Developmental disability is defined by federal law and can include many disabling conditions that qualify people for certain benefits. Some people have intellectual disability, some have developmental disabilities, and some have both. These terms are connected, but they don’t mean the same thing. IDD is a shortcut or hybrid term used by some agencies and organizations to include both people with ID and people with DD.
Plain Language Summary
Intellectual disability refers to significant limitations in intellectual functioning and adaptive behavior occurring before the age of 22. Developmental disability, as defined by the federal government, includes numerous conditions that start before adulthood. Some people with ID and DD need support with learning, communication, movement, decision-making, daily activities, or living in the community.
The words intellectual disability, developmental disability, and IDD are connected, but they don’t mean the same thing.
- Intellectual disability means a person usually needs support to learn, understand information, solve problems, or handle everyday tasks.
- Developmental disabilities is a broader term for certain conditions that start before age 22 and may affect daily life for a long time.
- IDD is a shorthand term sometimes used by agencies or organizations to plan for the broader community of people with intellectual disability and developmental disabilities, including people who have both.
The Arc has advocated for people with intellectual disability and developmental disabilities and their families for over 75 years, including in areas such as Medicaid, community living, education, civil rights, employment, future planning, and criminal justice.
Key Takeaways
- ID stands for intellectual disability.
- DD stands for developmental disability.
- IDD is a shorthand term for intellectual and developmental disabilities.
- Intellectual disability is a specific disability with clinical criteria.
- Developmental disability is a broader term used in law, public programs, planning, and services.
- Developmental disability is not one diagnosis.
- Some people have both intellectual disability and developmental disability.
- Some people have developmental disabilities but don’t have intellectual disability.
- Some people have intellectual disability but don’t have developmental disabilities.
- These terms matter because they can affect eligibility, services, supports, communication, education, healthcare, and civil rights protections.
- A diagnosis or label doesn’t define a person’s life, goals, relationships, or support needs.
What Is Intellectual Disability?
Intellectual disability is a disability that begins during the developmental period (before age 22) and involves significant limitations in both intellectual functioning and adaptive behavior.
- Intellectual functioning can include learning, reasoning, problem-solving, understanding information, and applying knowledge.
- Adaptive behavior means the everyday skills people use to communicate, make decisions, care for themselves, navigate relationships, participate in school or work, and live in the community. It’s often discussed in three areas: conceptual skills, social skills, and practical skills.
Intellectual disability may affect how a person learns, understands information, solves problems, communicates, or handles parts of daily life.
People with intellectual disability are part of every community. They learn, work, build relationships, make decisions, advocate, contribute, and pursue goals with the right supports.
How Is Intellectual Disability Diagnosed?
A diagnosis of intellectual disability isn’t based on one test score alone. A full evaluation looks at intellectual functioning, adaptive behavior, age of onset, and the person’s support needs.
For a diagnosis of intellectual disability, professionals usually look at:
- intellectual functioning
- adaptive behavior
- when the disability began
- the person’s support needs
What Is Adaptive Behavior?
Adaptive behavior means the everyday skills people use to communicate, make decisions, care for themselves, navigate relationships, participate in school or work, and live in the community. Adaptive behavior matters because it helps identify what supports a person may need in real life.
Adaptive behavior is often discussed in three areas: conceptual skills, social skills, and practical skills.
- Conceptual skills can include language, reading, writing, money, time, number concepts, problem-solving, and self-direction.
- Social skills can include communication, relationships, social judgment, following rules, understanding risk, and navigating different social situations.
- Practical skills can include personal care, transportation, home life, work, safety, health routines, using technology, and daily decision-making.
What Are Developmental Disabilities?
Developmental disability is a broad term used in law, public programs, planning, and services. Developmental disability is not a diagnosis.
In everyday words, developmental disability means a disability starts before adulthood and may affect a person’s daily life for a long time.
Under the federal Developmental Disabilities Assistance and Bill of Rights Act, developmental disability is generally defined as a severe, chronic disability that begins before age 22, is likely to continue indefinitely, and results in substantial limitations in major areas of life.
The federal DD criteria also include that the individual has substantial limitations in three of the following areas of major life activity:
- self-care
- receptive and expressive language
- learning
- mobility
- self-direction
- capacity for independent living
- economic self-sufficiency
The federal definition also specifies that developmental disability reflects the individual’s need for individually planned and coordinated supports or other assistance that are lifelong or of extended duration.
Developmental disabilities are broad. Two people with developmental disabilities may have very different diagnoses, communication styles, support needs, and life goals.
How Are Developmental Disabilities Identified for Services?
Developmental disability is not a diagnosis. Public programs may use different rules to decide whether a person qualifies for developmental disability services or supports.
Programs may look at:
- whether the disability began before age 22
- whether it’s likely to continue indefinitely
- how it affects major life activities
- what long-term services or supports the person needs
A medical diagnosis, school evaluation, Medicaid waiver assessment, or state developmental disability services process may use different rules. Families should check the requirements for the specific program or service they are applying for.
Examples of Developmental Disabilities
Developmental disabilities can include many different diagnoses and conditions, such as:
- autism
- cerebral palsy
- Down syndrome
- epilepsy
- Fragile X syndrome
- fetal alcohol spectrum disorders
- genetic conditions
- brain injuries that occur during the developmental period
- intellectual disability
- other conditions that begin during the developmental period and result in substantial functional limitations
This isn’t a complete list and a diagnosis alone doesn’t tell you what a person needs, what they can do, how they communicate, or what support will help them live the life they choose. Support should be individualized.
What Does IDD Mean?
IDD stands for intellectual and developmental disabilities.
The term is sometimes used as a shorthand term by agencies or organizations that plan for the broader community of people with intellectual disability and developmental disabilities, including people who have both.
IDD is an umbrella term for planning for people with ID, DD, and both ID and DD with many different disabilities, support needs, communication styles, and life experiences.
The IDD community can include people with:
- intellectual disability
- cerebral palsy
- Down syndrome
- epilepsy
- Fragile X syndrome
- fetal alcohol spectrum disorders
- genetic conditions
- brain injuries that occur during the developmental period
- other developmental disabilities
This list is not complete. A person’s diagnosis doesn’t tell the full story of their strengths, goals, relationships, or support needs. Two people with the same diagnosis may have very different support needs. Two people with different diagnoses may need similar supports.
Having ID and/or DD is also not a measure of a person’s worth, potential, personality, relationships, decision-making rights, or place in the community.
The most important question isn’t only what label is used. It’s what support the person needs to learn, communicate, make choices, participate in the community, and live safely.
What’s the Difference Between ID, DD, and IDD?
Intellectual disability, developmental disabilities, and IDD are related terms, but they shouldn’t be used as if they mean the same thing.
| Term | Plain-Language Meaning | Key Point |
|---|---|---|
| Intellectual disability, or ID | A disability that can affect learning, understanding, problem-solving, and everyday skills | ID is a specific disability with clinical criteria |
| Developmental disability, or DD | A broad term for numerous conditions that start before age 22 and may affect daily life for a long time | DD is not one diagnosis |
| Intellectual and developmental disabilities, or IDD | A broad shortcut term used by some agencies and organizations when talking about the broader community of people with intellectual disability and developmental disabilities, or when referring to people who have both ID and DD | Some people have both ID and DD, while others have only one |
Using the right term matters. It can affect services, eligibility, support planning, communication, and how people are understood by schools, agencies, healthcare providers, policymakers, and communities.
Can Someone Have Both Intellectual Disability and Developmental Disability?
Yes. Some people have both intellectual disability and a developmental disability.
Some people have a developmental disability, such as autism, cerebral palsy, epilepsy, or another condition, but don’t have intellectual disability.
Some people have intellectual disability and also meet the definition of a developmental disability.
This is why ID, DD, and IDD shouldn’t be used as if they mean the same thing.
Why These Terms Matter
The determinations of intellectual disability or developmental disability can affect whether a person qualifies for services, what supports are offered, how schools and agencies document needs, and how professionals understand a person’s rights.
Using the right term helps people get the right support. Using the wrong term can create confusion, limit access to services, create problems in people’s lives, or erase important differences between people with different needs.
The Terms Can Affect Eligibility
These definitions can affect eligibility for:
- Medicaid home and community-based services
- state developmental disability services
- special education
- Social Security benefits
- vocational rehabilitation
- housing supports
- transportation services
- healthcare supports
- criminal justice accommodations
- long-term services and supports
Eligibility rules can vary by program and state. A person may qualify for one service but not another, even when their support needs are real and significant.
The Terms Can Affect Support Planning & Public Understanding
A diagnosis doesn’t tell the whole story. Two people with the same diagnosis may have very different support needs, and two people with different diagnoses may need similar supports.
Support planning should focus on the person, not only the label. Clear language also helps families, educators, policymakers, service providers, and communities better understand who is included and what support may be needed.
What ID and DD Are Not
Intellectual disability and developmental disability aren’t the same as mental illness, dementia, or a temporary medical condition.
People with intellectual disability or developmental disabilities can have co-occurring mental health conditions, chronic health conditions, learning disabilities, sensory disabilities, or other disabilities. These conditions can sometimes be missed or misunderstood, especially when communication, fear, trauma, or difficulty understanding treatment options affects how a person explains what they’re experiencing.
People should be able to get support for all parts of their lives, including accessible healthcare, mental health, disability services, and accommodations when needed.
Language Guidance: How to Talk About ID, DD, and IDD
Language matters because it shapes what benefits people can receive and how people are understood and treated.
The Arc uses:
- ID for intellectual disability
- DD for developmental disability
- IDD as a simple shortcut for intellectual and developmental disabilities
Use ID when referring specifically to intellectual disability. When referring specifically to intellectual disability, use the singular term: person with intellectual disability.
Use DD when referring specifically to developmental disability or developmental disabilities.
Use IDD as an organization or agency shortcut when referring to the broader community of people with intellectual disability and developmental disabilities, or when referring to people who have both intellectual disability and a developmental disability.
When possible, be specific and accurate. If you mean autism, say autism. If you mean intellectual disability, say intellectual disability. If you mean developmental disability, say developmental disability.
Words and Phrases to Avoid
Some words and phrases are outdated, harmful, vague, or euphemistic. They can make disability sound shameful or reduce people to stereotypes.
Avoid:
- the R-word
- special needs
- handicapped
- differently abled
- suffers from
- afflicted with
- victim of
- wheelchair-bound
- high-functioning or low-functioning
Get more guidance on language from the ASU National Center on Disability and Journalism.
Rights and Supports for People With ID & DD
People with ID and DD have the same rights as anyone else. They have the right to live in the community, go to school, work, make choices, access healthcare, build relationships, and participate in public life.
Many people with ID and DD also need services or accommodations to make those rights real in daily life. Supports may come through schools, Medicaid, state developmental disability agencies, employers, healthcare providers, transportation systems, housing programs, families, and community organizations.
This is why definitions matter. The words and the diagnosis used to describe a disability can affect whether a person gets access to the services and supports they need.
How The Arc Supports People With ID, DD, and Families
The Arc advocates for and supports people with intellectual disability and developmental disabilities and their families across the lifespan.
That includes work on:
- Medicaid and home and community-based services
- special education and IEP rights
- employment
- future planning
- technology
- travel
- criminal justice
- civil rights
- healthcare
- housing
- financial stability
- family support
- community inclusion
Through our national office and chapter network, The Arc works to protect rights, expand access to services, and support people with ID and DD in building lives of their choosing.
Frequently Asked Questions About Intellectual Disability & Developmental Disabilities
Is intellectual disability the same as developmental disability?
No. Intellectual disability is a specific disability involving significant limitations in intellectual functioning and adaptive behavior. Developmental disability is a broader term that can include intellectual disability and many other disabilities and conditions.
Can someone have a developmental disability without intellectual disability?
Yes. Some people have developmental disabilities but do not have intellectual disability. For example, a person may have cerebral palsy, epilepsy, autism, or another developmental disability without meeting the criteria for intellectual disability.
Can someone have both intellectual disability and developmental disability?
Yes. Some people meet the definitions of both intellectual disability and developmental disability.
What is the difference between ID, DD, and disability?
Disability is a broad term that can include many physical, sensory, mental health, intellectual, developmental, and other disabilities. ID refers specifically to intellectual disability, and DD refers to developmental disabilities.
What does IDD stand for?
IDD stands for intellectual and developmental disabilities. It is a shortcut term used by some agencies and organizations to refer to the broader community of people with intellectual disability and developmental disabilities, including people who have both.
Is autism the same as intellectual disability or developmental disability?
Autism is generally considered a developmental disability. Some autistic people also have intellectual disability, and some do not.
Is Down syndrome the same as intellectual disability or developmental disability?
Down syndrome is generally considered a developmental disability. Many people with Down syndrome also have intellectual disability, but support needs vary by person.
Is developmental disability a diagnosis?
No. Developmental disability is a broad term used in some laws, public programs, planning, and services. It can include many different diagnoses and conditions.
What is adaptive behavior?
Adaptive behavior refers to the everyday conceptual, social, and practical skills people use in daily life, such as communication, decision-making, personal care, relationships, safety, and community participation.
What supports may help people with ID and DD?
Supports may include special education, Medicaid home and community-based services, employment supports, transportation, assistive technology, communication supports, healthcare coordination, future planning, housing support, and help with daily life. The right supports depend on the person.
Can adults have ID and DD?
Yes. Intellectual disability and developmental disabilities begin before adulthood, but with supports, people with ID and DD can function better. Support needs can change over time, and people should have access to support across their lives.
What is the difference between a diagnosis and support needs?
A diagnosis can help explain a disability and may affect eligibility for services. Support needs describe what helps a person live, learn, communicate, make decisions, work, and participate in the community. Two people with the same diagnosis may have different support needs.
Are learning disabilities part of ID and DD?
Sometimes, but not always. A specific learning disability, such as dyslexia or dyscalculia, isn’t automatically the same as intellectual disability or developmental disability. But people with ID and DD may also have learning disabilities, and some people may qualify for developmental disability services depending on when the disability began, how it affects daily life, and what support the person needs.
Is intellectual disability the same as mental illness?
No, intellectual disability isn’t the same as mental illness. But many people with ID and DD also have mental health conditions and should be able to get mental health support that’s accessible and appropriate.
Why does The Arc use the term IDD?
The Arc uses IDD when referring to planning for the broader community of people with intellectual disability and developmental disabilities, including people who have both. The term reflects the community The Arc advocates for and supports.
Sources
- Intellectual Disability and Developmental Disabilities: Clarifying Terminology
- Need for Stability and Predictability in Terminology in Times of Change and Challenges
- American Association on Intellectual and Developmental Disabilities: Definition of Intellectual Disability
- Developmental Disabilities Assistance and Bill of Rights Act
- National Institutes of Health: Intellectual and Developmental Disabilities
Written by: Marty Ford, Senior Advisor, The Arc of the United States and Ruth Luckasson, Distinguished Professor Emerita of Special Education, University of New Mexico
The Arc promotes and protects the human rights of people with intellectual and developmental disabilities and actively supports their full inclusion and participation in the community throughout their lifetimes.
