The process and correlates of addiction prior to treatment are examined for a sample of 546 women and men methadone maintenance clients. Narcotic addiction careers for women (defined both as from first daily use to first treatment intervention, and from first daily use to last daily use of heroin) were shorter than those for men, and women entered treatment earlier. However, the narcotic drug use patterns for women were not substantially different from those for men (including mean percentage of time using, number of times abstinent, number of relapses, and so forth). Narcotics use for many women was influenced by a spouse or partner, but some also reported increased use for hedonistic reasons. Criminal behaviors increased for both women and men after addiction, and the major sex difference was the type of crime committed. Differences for women and men for employment, welfare, and interpersonal relationships reflected patterns found in the larger society.