The prevalence of psychiatric morbidity in mentally retarded adults.

302 mentally retarded adults, sampled by epidemiological criteria, were examined with regard to handicaps, behaviour, skills and psychopathology by use of the MRC HBS-schedule and a list of psychiatric items. Based on research criteria, a computerized psychiatric diagnosis was made on a hierarchial scale. A psychiatric disorder was diagnosed in 85 (27.1%), which is a smaller prevalence rate than found in other studies. Next to behaviour disorder (10.9%), psychosis of uncertain type (5%) was the most common disorder. Dementia and early childhood autism were found equally often (3.6% each). Neurosis was seldom (2%), while schizophrenia (1.3%) and affective disorder (1.7%) occurred at about the same rates as found in similar investigations. No cases of alcohol or drug abuse were found.