OBJECTIVE: This study was designed to examine the relationship between reason for referral and subsequent DSM-III-R diagnosis in institutionalized individuals with severe to profound mental retardation. A heavy emphasis was placed on articulating how diagnostic criteria are applied in this population. METHOD: The study population consisted of 251 patients consecutively referred for initial psychiatric consultation from a large series of institutionalized patients with predominately severe to profound mental retardation. On the basis of the chief complaint, subjects could be grouped into six overlapping categories: self-injury, aggression, hyperactivity, agitation, medical questions, and miscellaneous behaviors. Psychiatric diagnoses were made according to DSM-III-R criteria on the basis of simultaneous clinical examination, staff interview, and medical review. Relevant medical conditions were noted. RESULTS: The authors demonstrate, as have others, that it is possible to make psychiatric diagnoses in this population and that psychiatric disorder is common. The most frequent diagnoses were impulse control disorders, anxiety disorders, and mood disorders. Comorbid medical conditions, particularly seizure disorders, are also common. CONCLUSIONS: These results are consistent with the reported experience of others and underscore the importance of psychiatric involvement in the multidisciplinary assessment and treatment of individuals with retardation.