A multidisciplinary diagnostic evaluation was performed for 868 older psychiatric inpatients during a 46-month interval. A total of 402 (46%) met DSM-III-R criteria for organic mental disorders, 329 (38%) had mood disorders, 90 (10%) had psychotic disorders, and 47 (5%) had other mental disorders or conditions. Concurrent medical problems were systematically assessed and classified according to ICD-9-CM criteria. The patients suffered from a mean of 5.6 +/- 3.1 (SD) active medical problems (range 0-18). This level of medical comorbidity was significantly greater than that of older psychiatric outpatients and comparable to that of elderly inpatients in general medical hospitals. When the effects of age and education were controlled for, there were no significant differences in mean numbers of medical problems among the four groups of psychiatric inpatients. An association of major depression with diseases of the digestive system was observed and may be related to peripheral autonomic dysregulation.