Key Points Intellectual disability (ID) is characterized by limitations in both intelligence and adaptive skills.It begins in childhood and is usually identified by failing to meet expected developmental milestones during routine visits.ID is classified on the basis of level of function, as being mild, moderate, severe, or profound. Most individuals with ID are in the mild category.Most cases of ID are multifactorial, although underlying genetic and metabolic disorders can be causative.Children with ID are likelier to have other neurodevelopmental disorders such as autism, attention-deficit/hyperactivity disorder, or learning disabilities.Treatment goals are to lessen the effects of the disability and optimize functioning in the child’s everyday life. Access to early intervention programs is highly important so that the child and family can receive appropriate support.Children with ID are at increased risk for poverty and poor health outcomes as adults. Long-term outcomes are related to the severity of ID.