Mental illness and mental retardation: cause or coincidence?

A sample of 93 patients admitted to an inpatient psychiatric unit for emotionally disturbed, developmentally disabled adolescents was studied in an attempt to clarify the relationship between intellectual functioning and psychoses occurring in the developmental period. The severity and duration of the psychosis, the presence of hallucinations, and the degree of isolation of the child from his or her environment appear to be important factors influencing the occurrence of decreased psychometric test scores in the individuals studied.