Two hundred ninety-eight treatment-seeking and 101 community cocaine abusers were interviewed using the Schedule for Affective Disorders and Research Diagnostic Criteria. Alcoholism was the most frequently diagnosed current and lifetime psychiatric disorder in both samples. Several findings from this study converge with recent evidence which suggests a particularly strong relationship between cocaine abuse and alcoholism that may differ from other types of alcohol-drug comorbidity. First, rates of alcoholism among cocaine abusers doubled those of comparable samples of opioid addicts. Second, while virtually all cocaine abusers in this sample reported some alcohol use during the past month, a lifetime diagnosis of alcoholism was associated with more severe cocaine dependence. Third, the onset of alcoholism followed the onset of drug dependence for the majority of alcoholic cocaine abusers, a pattern which contrasts that typically seen in other types of drug-alcohol comorbidity and suggests that cocaine abuse may increase vulnerability to secondary alcoholism. Prognostically, cocaine abusers who were alcoholic at baseline interview were more likely to remain alcoholic at 1-year follow-up but did not differ from nonalcoholic cocaine abusers on other measures of outcome.