Literature searches were conducted in 13 databases. The first section of this article reports on findings regarding a comparison of the background characteristics of men and women with substance-use problems. Research findings are summarized for gender differences of drug users in socioeconomic status, drug-use patterns, family and abuse histories, criminal histories, and mental health issues. The second section addresses literature that deals with drug treatment outcomes by gender, with a focus on women. Studies that have examined drug use by gender during or after treatment have found that either there was no significant difference in outcomes between men and women or that women had more favorable outcomes than men. Studies that examined criminal activity as an outcome measure found that gender was not a significant predictor, that women had a lower pretreatment to posttreatment reduction in crime severity, or that women had lower arrest or recidivism rates. The review concludes that much research remains to be done in adequately addressing the issue of what components of drug treatment are necessary to ensure positive outcomes for females. Outcome studies do not address whether the programs would have had more or less success among women in gender-specific interventions, since such studies rarely mention gender-specific issues. Research has not systematically addressed whether women have better outcomes when treated in all-women programs compared to mixed-gender programs. Six suggestions are offered for objectives in future research on gender issues in drug treatment. 1 table and 109 references