The relationship between psychoactive drug abuse and psychopathology is complex. There have been few systematic explorations of substance abuse in psychiatric populations since the recent epidemic of cocaine abuse. To update and further explore the relationship between psychiatric illness and substance abuse, 100 consecutively admitted patients to an inpatient psychiatry unit were administered a drug and alcohol use/abuse questionnaire. Sixty-four percent endorsed current or past problems with substance abuse and 29% met DSM-III-R criteria for substance abuse in the 30 days prior to admission. For the major diagnostic categories, there were no significant differences between groups in percentages of patients with substance abuse disorders. There was a trend (p less than or equal to .2) toward an increased number of lifetime psychiatric hospitalizations in the substance-abusing group. Alcohol was the most common drug of choice followed by stimulants, cannabis, and sedative hypnotics. Differences in drug choices between diagnostic categories are discussed. Forty-three percent of urine drug screens obtained were positive, and of those with positive urine drug screens, 42% denied drug use upon admission. Only 40% of patients with current or past substance abuse problems had received treatment for their chemical dependency. In our sample, while substance abuse was very prevalent, it was underreported and undertreated.