OBJECTIVE: To compare a mindfulness-based intervention with cognitive behavioral therapy (CBT) for the group treatment of anxiety disorders. METHOD: One hundred five veterans (83% male, mean age=46 years, 30% minority) with one or more DSM-IV anxiety disorders began group treatment following randomization to adapted mindfulness-based stress reduction (MBSR) or CBT. RESULTS: Both groups showed large and equivalent improvements on principal disorder severity thru 3-month follow up (ps<.001, d=-4.08 for adapted MBSR; d=-3.52 for CBT). CBT outperformed adapted MBSR on anxious arousal outcomes at follow up (p<.01, d=.49) whereas adapted MBSR reduced worry at a greater rate than CBT (p<.05, d=.64) and resulted in greater reduction of comorbid emotional disorders (p<.05, d=.49). The adapted MBSR group evidenced greater mood disorders and worry at Pre, however. Groups showed equivalent treatment credibility, therapist adherence and competency, and reliable improvement. CONCLUSIONS: CBT and adapted MBSR were both effective at reducing principal diagnosis severity and somewhat effective at reducing self-reported anxiety symptoms within a complex sample. CBT was more effective at reducing anxious arousal, whereas adapted MBSR may be more effective at reducing worry and comorbid disorders.