The clients in an institution for the mentally retarded were screened for signs of psychopathology with the Psychopathology Instrument for Mentally Retarded Adults (PIMRA). Of the 168 clients, 146 satisfied criteria for DSM–III axis I disorders, and 153 satisfied criteria for at least one disorder on either axis I or II. Multiple diagnoses were common, and a total of 288 diagnoses were found. No particular disorder was found to be more prevalent in those with organic brain dysfunction. The level of functioning was not found to predispose to any particular diagnosis. There was a positive relationship between the presence of a psychiatric disorder and the resources available to the clients and the activities offered. The prevalence of psychiatric disorders was extremely high in the population studied, with the exception of the affective disorders, of which no case was found. One possible reason for this high prevalence is that deinstitutionalisation leaves behind those with the more severe behavioural problems.