OBJECTIVE: This study examined baseline self-efficacy as a moderator of outcomes comparing women receiving either the Women's Recovery Group (WRG), a new manualized group treatment for substance use disorders combining single-gender group composition and women-focused content, or Group Drug Counseling (GDC), an empirically supported mixed-gender group treatment. METHODS: To understand the relationship of baseline scores of abstinence self-efficacy measured by the Drug-Taking Confidence Questionnaire (DTCQ) to outcome, we included the interaction of group by phase by continuous DTCQ scores in the outcome analyses. Women were split into groups of high versus low abstinence self-efficacy based on the clinical cutoff score of 80 on DTCQ. RESULTS: We found a significant 3-way interaction effect of treatment condition, time, and baseline DTCQ scores on drinking days and days of any substance use per month. Women in WRG had greater reduction in substance use from baseline to post-treatment than women in GDC, and women in WRG with low self-efficacy had the best outcomes overall. CONCLUSION: The findings suggest that women with low self-efficacy may have enhanced treatment outcomes in a single-gender substance use treatment group.