The frequent co-occurrence of alcoholism with serious mental illnesses (“dual diagnosis”) necessitates that clinicians are able to recognize its presence in people with disabling mental illnesses. This study demonstrates that professionals often miss the diagnosis, but that their ability to detect alcoholism can be greatly enhanced by the use of a simple screening tool. Members of an urban psychosocial rehabilitation program who received psychiatric treatment in an affiliated outpatient clinic were interviewed after their clinic therapists and rehabilitation counselors had been asked questions pertaining to their general health and substance use. The members were interviewed with two screening tests, the CAGE and the SMAST, and a clinical DSMIII-R diagnosis of alcohol use disorder was established. Both the SMAST and CAGE had good sensitivity and the addition of a screener enhanced the clinicians' ability to detect alcohol use disorders.