This study examines the prediction of substance-related technical violations and arrests from (a) a three-dimensional measure of substance abuse treatment engagement—treatment satisfaction, treatment participation, and counselor rapport—and (b) support from peers in the treatment program. The study focuses on 204 women on probation or parole who attended a substance abuse treatment program in the first 9 months of supervision. Data were collected in face-to-face interviews and from official records of violations and arrests. Generalized linear mixed-effects modeling was used to assess the main effects and the interaction effect of within-program peer support and other indicators of engagement as predictors of substance-related technical violations and arrests. Peer support was positively related to violations/arrests when treatment engagement was low. Findings suggest that for women who do not score high in treatment engagement, support from peers is related to increased recidivism, and group treatment may be contraindicated.