A substantial number of women who enter substance abuse treatment have a history of trauma and meet criteria for posttraumatic stress disorder (PTSD). Fear regarding the extent to which PTSD treatment can evoke negative consequences remains a research question. This study explored adverse events related to the implementation of an integrated treatment for women with trauma and substance use disorder (Seeking Safety) compared with a nontrauma-focused intervention (Women's Health Education). Three hundred fifty-three women enrolled in community substance abuse treatment were randomized to 1 of the 2 study groups and monitored weekly for adverse events. There were no differences between the two intervention groups in the number of women reporting study-related adverse events (28 [9.6%] for the Seeking Safety group and 21[7.2%] for the Women's Health Education group). Implementing PTSD treatment in substance abuse treatment programs appears to be safe, with minimal impact on intervention-related adverse psychiatric and substance abuse symptoms. More research is needed on the efficacy of such interventions to improve outcomes of PTSD and substance use.