Primary alcoholics may display symptoms of affective or psychotic disorders, while mentally ill patients may develop persistent alcohol-related problems. The author discusses the importance of distinguishing alcoholic psychosis from schizophrenia and alcohol-induced confusion from organic brain syndrome. He then outlines the diagnosis and treatment of other alcohol-induced conditions such as alcoholic dementia, antisocial behavior, and drug abuse. After stressing that primary alcoholism can mimic almost any psychiatric disorder, and secondary alcohol abuse can exacerbate any psychiatric symptoms, the author asserts that physicians should routinely include substance abuse as part of the differential diagnosis of psychiatric patients.