Intellectual disability is a condition characterized by significant limitations in intellectual functioning and in adaptive behavior, originating before the age of 18. An intelligence score of approximately 70 or below is a common benchmark, yet diagnosis also requires impairment in everyday skills such as communication, self-care, and social participation.

Causes are diverse. Genetic conditions such as Down syndrome and fragile X syndrome, prenatal exposure to toxins or infection, birth complications, and severe early deprivation can all produce intellectual disability. In many cases no single cause is identified. The degree of limitation ranges from mild—where independent living with support is often possible—to profound, requiring continuous care.

Early intervention, special education, and community supports improve outcomes. The focus of modern practice is on maximizing adaptive functioning and inclusion rather than on the IQ number alone. Legal and educational definitions have shifted over time, reflecting both scientific understanding and changing social values.

Intellectual disability is a developmental condition that affects the acquisition of cognitive and practical skills. Support and opportunity shape how fully a person’s potential is realized.