Background: The treatment of substance abuse in secure settings needs to be informed by gender specific considerations. Aim: To assess the effectiveness of a manualised CBT substance abuse treatment programme designed for women in medium security. Method: Assessment of pre-post changes following treatment using substancespecific and other outcome indicators. Results: Positive outcomes were identified for treatment completers (n ¼ 23) in terms of improved substance-related self-efficacy, lower perceived costs and greater benefits of change. These differences, which were not evident in the non-completer group (n ¼ 11), were paralleled by positive clinical changes on subscale of the BPRS, CANFOR needs and increased general self-efficacy. Conclusions: Treatment was successful in engaging two-thirds of patients to complete treatment in readiness for conditions of lower security and potential exposure to alcohol and other drugs. Differences between completers and non-completers raise issues about the timing and intensiveness of treatment at stages in treatment paths for women in secure settings.