Although alcohol use disorders are commonly associated with co-morbid drug use and psychiatric disorders, such co-morbidity is frequently underdiagnosed and inadequately treated. This paper reviews the epidemiological, diagnostic, and treatment literature on the co-morbidity of alcoholism, with a focus on the most common co-morbid disorders: drug abuse, mood disorders, anxiety disorders, and antisocial personality disorder. The paper goes on to describe a number of promising approaches to the treatment of these common co-morbid disorders in alcoholics. Despite the difficulties inherent in treating dual diagnosis patients, the clinician must recognize that it is possible to derive valid diagnoses and deliver efficacious treatment to such patients.