The prevalence and type of substance abuse and dependence were determined for 49 patients with mood disorders on a general hospital psychiatric unit. A standardized diagnostic interview was conducted with a high value of inter-rater reliability. This study found that 18.4% of mood disorder inpatients met the diagnostic criteria for psychoactive substance use disorders by DSM-III-R. Sedatives-hypnotics-anxiolytics was the most common substance use disorder (10.2%), followed by alcohol (6.1%). Patients with major depression had a higher rate of comorbidity with substance use disorders than did the bipolar disorder patients (p = 0.011). The prevalence of sedatives-hypnotics-anxiolytics use disorder among major depression patients was 35.7%, which was higher than that among bipolar disorder patients (0%). Male patients had a significantly higher percentage of substance use disorders than did female patients (p = 0.054). Seventy-seven percent of the patients with a dual diagnosis of mood and substance use disorder were not diagnosed as having substance use disorders by psychiatrists in charge.