Abstract The present study investigated the incidence of attention deficit hyperactivity disorder in a sample of 86 adults with severe to profound mental retardation. Participants were evaluated by supervisory staff using the diagnostic criteria from the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) and Conners’ (1990) Hyperactivity Index. Using the most conservative measure, 15% of the sample met the diagnostic criteria. This measure was not influenced by the subjects’ chronological age, adaptive age, IQ, or gender. Implications of this finding for continued research and practice were discussed.