Abstract: Objective: Veterans returning from deployment have high rates of posttraumatic stress disorder (PTSD) and co-occurring alcohol use disorder (AUD). Current treatments for PTSD and AUD report high dropout rates, and many veterans report alcohol misuse to cope with symptoms of PTSD. The present study is a pilot randomized controlled trial in which veterans (N = 201) were randomized to receive a mobile mindfulness-based intervention enhanced with brief alcohol intervention content (Mind Guide) or an active stress management program. Method: To be eligible for the study, veterans had to have served after September 11, 2001 (post-9/11 veteran) and screen positive for PTSD and AUD. All participants were asked to complete a baseline and four monthly follow-up assessments (two during treatment phase and two posttreatment phase). Primary outcomes were PTSD symptoms, frequency of alcohol use, and alcohol use consequences. Results: Engagement with Mind Guide was excellent (averages of over 31 logins and 5 hr of app usage). Those assigned to Mind Guide showed significant reductions in PTSD symptoms (d = -0.36; 16-week follow-up). No differences emerged for frequency of alcohol use (d = -0.12; 16-week follow-up) or consequences (d = -0.12; 16-week follow-up). Conclusions: Mind Guide may be a valuable adjunct to more intensive in-person PTSD treatment by facilitating interest in services, integration into care, and/or sustainment of posttreatment improvements. Further development of Mind Guide may enhance efficacy at reducing alcohol use and consequences.