Comparisons of behaviors during treatment were made between a sample of women and a sample of men methadone maintenance clients. Women in this study exhibited high motivation for treatment. Overall, however, small differences were found between the sexes with respect to treatment process and outcome measures. The observed differences that were significant included use of substances other than heroin, interpersonal relationships, drug dealing, employment, and criminal behaviors. The differences seemed to be in accordance with traditional sex role expectations. The distinctive behavior pattern of Chicanas demonstrated in this study demands special attention. It is suggested that treatment programs should incorporate more services to meet women-specific needs.