Introduction: Substance use is increasingly prevalent among women. Little research examines subgroups of women with substance use issues to identify their characteristics and thus enable treatment recommendations. The present study used latent class analysis to identify subgroups of substance use among women in substance-use treatment based on use in the 30 days prior to intake and examined changes in mental health and treatment outcomes following 60 days of treatment. Methods: Participants were women (N = 493) attending specialist non-government substance use treatment services in New South Wales, Australia. Results: Four distinct classes of substance users were identified: (i) Amphetamine Type Stimulants (ATS) Polysubstance (40.6%, n = 200); (ii) Alcohol Only (33.1%, n = 163); (iii) Cannabis and Alcohol (17.0%, n = 84) and (iv) Other Polysubstance (9.3%, n = 46). Women in the ATS Polysubstance class were the youngest and those in the Alcohol Only class were the oldest. Discussion and Conclusions: Findings show that classes with high polysubstance use (ATS Polysubstance) differed from the single-substance use class (Alcohol Only). The ATS Polysubstance class had significantly greater improvements in health outcomes after 60 days compared to the Alcohol Only class. These findings suggest that although women with polysubstance use can benefit from substance use treatment, younger women (ATS Polysubstance) may benefit even more than older women (Alcohol Only). Future research should utilise a longitudinal design and examine additional psychosocial characteristics to extend on current findings.