Up to 60% of women enrolled in substance use treatment meet criteria for both substance use disorder (SUD) and post traumatic stress disorder (PTSD), presenting with more severe clinical profiles and psychiatric disorders, higher relapse rates, and lower treatment gains and compliance with aftercare than women with either disorder alone. Although evidence suggests treating SUD and PTSD concurrently is most effective, few treatments have been developed for co-occurring SUD-PTSD, and even fewer have been validated on women. Moreover, in a population with disproportionately high relapse rates, minimal longer-term follow-up data limits knowledge of longitudinal treatment effects. Thus, the current application seeks to evaluate the sustainability of mindfulness practice and treatment gains following a Mindfulness-Based Relapse Prevention (MBRP) program for women with co-morbid SUD-PTSD. Specifically, we are interested in whether participants continue mindfulness practice following program completion, and if mindfulness practice predicts SUD- and PTSD-related outcomes. Using a smartphone application and evidence-based methods of collecting comprehensive follow-up data, women with SUD-PTSD currently enrolled in a pilot trial assessing efficacy of Trauma-Integrated MBRP will be administered assessments at 3-, 6-, 9-, and 12-months following treatment. Data collected from this research will further inform adaptation and implementation of MBIs for women with SUD-PTSD.