Veterans with posttraumatic stress disorder (PTSD) and substance abuse may abuse benzodiazepines and develop violent dyscontrol when using them. A total of 370 veterans were compared by substance abuse diagnosis (50%), benzodiazepine use (36%), and their interaction on 1-year outcomes after inpatient discharge. Substance abusers were less likely to be prescribed benzodiazepines (26% vs. 45%). No outcome showed a differential worsening by substance abuse or benzodiazepines, although some baseline differences were noted. Outpatient health care utilization was lower in benzodiazepine users (47 vs. 33 visits). Among PTSD patients with comorbid substance abuse, benzodiazepine treatment was not associated with adverse effects on outcome, but it may reduce health care utilization.