Objective: Understanding for whom, and under what conditions, treatments exert their greatest effects is essential for developing personalized medicine. Research investigating moderators of outcome among evidence-based treatments for anxiety disorders is lacking. The current study examined several theory-driven and atheoretical putative moderators of outcome in cognitive behavioral therapy (CBT) and acceptance and commitment therapy (ACT). Method: Eighty-seven patients with a "Diagnostic and Statistical Manual of Mental Disorders" (4th ed., text rev.; "DSM-IV-TR"; American Psychiatric Association, 2000) anxiety disorder completed 12 sessions of ACT or CBT and were assessed with a self-report measure of anxiety at baseline, post-treatment, and 6- and 12-month follow-up assessments. Results: CBT outperformed ACT among those at moderate levels of baseline anxiety sensitivity, and among those with no comorbid mood disorder. ACT outperformed CBT among those with comorbid mood disorders. Higher baseline neuroticism was associated with poorer outcome across treatment conditions. Neither moderation nor general prediction was observed for baseline anxiety disorder comorbidity, race/ethnicity, gender, age, or baseline severity of the principal anxiety disorder. When including all randomized participants who completed the pre-treatment assessment (N = 121), a similar pattern was observed. Conclusions: Prescriptive recommendations for clinical practice and directions for future research are discussed. (Contains 4 figures, 3 tables, and 4 footnotes.)