There is no single official list of “the five developmental disabilities.” The term covers a broad category of conditions that begin before age 22 and affect physical, cognitive, or behavioral development. That said, five conditions appear most frequently in public health literature and educational settings: intellectual disability, autism spectrum disorder, cerebral palsy, ADHD, and Down syndrome. About 1 in 6 children in the United States between ages 3 and 17 has at least one developmental disability.
What Counts as a Developmental Disability
Under federal law, a developmental disability is a severe, chronic condition that appears before age 22, is likely to continue indefinitely, and causes significant limitations in three or more areas of daily life. Those areas include self-care, language, learning, mobility, self-direction, independent living, and economic self-sufficiency. The definition is broad by design. It covers conditions rooted in physical impairment, cognitive impairment, or both.
For children under age 9, the threshold is lower. A child with a substantial developmental delay or a specific condition present at birth can qualify for services even before meeting the full criteria, as long as there is a high probability the child will meet them later.
Intellectual Disability
Intellectual disability involves below-average intellectual functioning (generally an IQ in the range of 65 to 75 or lower) combined with significant difficulty in everyday adaptive skills. Those skills fall into three broad areas: conceptual skills like reading and problem-solving, social skills like following rules and navigating relationships, and practical skills like personal hygiene and managing money.
Severity ranges widely. Some people with mild intellectual disability live independently with minimal support, hold jobs, and manage their own households. Others with more severe forms need daily assistance throughout their lives. Intellectual disability can result from genetic conditions, complications during pregnancy or birth, infections, or exposure to toxins. In many cases, no specific cause is identified.
Autism Spectrum Disorder
Autism spectrum disorder (ASD) affects how a person communicates, interacts socially, and processes the world around them. The CDC describes it as a developmental disability that can cause significant social, communication, and behavioral challenges. People with autism often have difficulty reading social cues, may prefer routines and become distressed by changes, and can show intense focus on specific interests.
The word “spectrum” matters here. Some autistic individuals need significant daily support, while others live fully independent lives and may not receive a diagnosis until adulthood. The American Academy of Pediatrics recommends specific autism screening at 18 months and again at 24 months, because early identification opens the door to therapies that can make a real difference in language development and social skills. Autism frequently co-occurs with intellectual disability, ADHD, or anxiety.
Cerebral Palsy
Cerebral palsy (CP) is a group of disorders that affect movement, muscle tone, and posture. It results from abnormal brain development or damage to the developing brain, most often before or during birth. CP is the most common motor disability in childhood.
There are four main types. Spastic cerebral palsy accounts for about 80% of cases and causes stiff muscles that make movements awkward or difficult. Dyskinetic cerebral palsy causes uncontrollable movements that can be slow and writhing or rapid and jerky, sometimes affecting the face and tongue enough to make swallowing and speaking hard. Ataxic cerebral palsy primarily affects balance and coordination, making fine motor tasks like writing a challenge. Mixed cerebral palsy involves symptoms of more than one type, most commonly a combination of spastic and dyskinetic.
CP varies enormously in severity. Some children walk independently with only slight stiffness in one leg. Others use wheelchairs and need help with most daily activities. Cognitive ability is not necessarily affected. Many people with cerebral palsy have typical intelligence.
ADHD
Attention-deficit/hyperactivity disorder is one of the most common neurodevelopmental conditions in children. It involves a persistent pattern of inattention, hyperactivity, impulsivity, or a combination of all three that interferes with functioning at home, school, or work. Symptoms must be present before age 12, show up in at least two settings, and go beyond what’s typical for a child’s developmental level.
ADHD is sometimes left off lists of developmental disabilities because many people with ADHD do not experience the “substantial functional limitations” required by the federal definition. For those who do, particularly when ADHD is severe or co-occurs with learning disabilities, it clearly fits the criteria. The CDC includes ADHD among the developmental disabilities it tracks. Children and adults with ADHD may struggle with organization, following through on tasks, waiting their turn, and managing time, but with the right support, most function well in school and careers.
Down Syndrome
Down syndrome is the most common chromosomal cause of intellectual disability. It occurs when a person has a full or partial extra copy of chromosome 21, which affects physical and cognitive development. Characteristic features include low muscle tone, a flat facial profile, and upward-slanting eyes, though these vary from person to person.
Most people with Down syndrome have mild to moderate intellectual disability. Many attend mainstream schools, hold jobs, and develop strong social skills. Health complications are common and can include heart defects, hearing problems, thyroid conditions, and a higher risk of early-onset Alzheimer’s disease. Life expectancy has increased dramatically over the past several decades, now averaging about 60 years in countries with good medical care.
Screening and Early Identification
The American Academy of Pediatrics recommends formal developmental screening for all children at 9 months, 18 months, and 30 months during routine well-child visits. These screenings use standardized questionnaires to flag potential delays in movement, language, thinking, and social skills. They are not diagnostic on their own but help identify which children need a closer look.
Early identification matters because the brain is most responsive to intervention in the first few years of life. Under the Individuals with Disabilities Education Act (IDEA), infants and toddlers with developmental delays or diagnosed conditions qualify for early intervention services starting at birth. These services, which can include speech therapy, physical therapy, and family coaching, are individually planned and provided at no cost to families. Children who receive early support consistently show better outcomes in language, social development, and school readiness compared to those identified later.
Overlap and Co-Occurring Conditions
Developmental disabilities rarely exist in isolation. A child with cerebral palsy may also have an intellectual disability. A child with autism may also have ADHD. Down syndrome almost always involves some degree of intellectual disability. National surveys reflect this complexity: when the CDC tracks developmental disabilities in children, it accounts for the fact that a single child may carry more than one diagnosis.
This overlap is one reason the search for a tidy list of exactly five conditions can be misleading. The federal definition focuses on functional limitations rather than specific diagnoses, recognizing that the real question is how much support a person needs to participate fully in daily life. Two people with the same diagnosis can have vastly different experiences depending on severity, co-occurring conditions, and the support systems around them.