Five-hundred-sixty-seven heroin addicts admitted to methadone maintenance treatment programs in southern California were included in the present analysis. Systematic comparisons were made between women and men for Anglo and Chicano subpopulations. The behaviors compared focused on initial drug use and other antecedent behaviors during the year prior to initiation of heroin use including interpersonal relationships, other substance use, drug dealing, legal income, and various criminal behaviors. Unlike men, the initial use of heroin by women was highly influenced by a man, especially by a sex partner who is often a daily heroin user. On the other hand, many women (like men) reported self-initiation of heroin use, multiple drug use, and drug dealing, thus demonstrating that they took an active role in their drug involvement. Other differences between men and women for antecedent behaviors prior to narcotics use appear to be related to traditional expectations about gender roles in American society.