According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR), diagnosis of an intellectual developmental disorder includes intellectual and adaptive functioning deficits with onset during the developmental period of life. The following three criteria must be met:
- Deficits in intellectual functioning, such as reasoning, problem solving, judgment, academic learning confirmed by a clinical assessment and standardized intelligence testing.
- Deficits in adaptive functioning in which the individual cannot meet developmental and social standards for independent living and social responsibility. Without ongoing support, the deficits limit functioning in one or more areas of daily living across several environments.
- The onset of intellectual and adaptive deficits occur during the developmental period.
There are four severity levels: