The DASH scale was used to assess 506 profoundly and severely mentally retarded persons (247 females and 259 males). The scale, covering 13 major psychiatric disorders, consists of 83 items derived from DSM-III-R as well as previously published studies of this population. Data were collected on symptom frequency, duration and severity in individual interviews with direct-care staff. Elimination and pervasive developmental disorders were most frequent, self-injurious behaviour disorders most severe. Most symptoms had been evident for at least a year. Inter-rater reliability was generally good.