OBJECTIVE: Mindfulness based relapse prevention (MBRP) has demonstrated efficacy in alleviating substance use, stress, and craving but how MBRP works for marginalized young adults has not been investigated. The current study used a novel rolling group format for MBRP as an additional intervention for young adults in residential treatment. We tested the hypothesis that MBRP (plus Treatment as usual (TAU)) would reduce stress, craving, and substance use among young adults in residential treatment relative to treatment-as-usual plus 12-step/self-help meetings (TAU only). Further, we examined whether reduced stress during treatment was a potential mechanism of change operating in MBRP. METHOD: Seventy-nine young adults (M RESULTS: At treatment completion young adults receiving MBRP had lower substance use (d = -0.58, [-0.91, -0.26]), craving (d = -0.58, [-1.0, -0.14]), and stress (d = -0.77 [-1.2, -0.30]) relative to TAU condition. Reduced stress during treatment partially mediated observed outcome differences between MBRP and TAU for substance use (β CONCLUSIONS: Results suggest that MBRP is a useful and appropriate intervention for marginalized young adults. Further, our results suggest that the effects of MBRP on long-term substance use outcomes may be partially explained by reduced stress.