Cognitive-behavioral therapy (CBT) and pharmacotherapy demonstrate efficacy across the anxiety disorders, but recognition of their limitations has sparked interest in combining modalities to maximize benefit. This article reviews the empirical literature to examine whether combining treatments influences efficacy of either monotherapy. We conducted a comprehensive literature search of published randomized trials that compared combined treatment with pharmacologic or CBT monotherapies. Ten studies that met our inclusion criteria were reviewed in detail, and within-subjects effect sizes were calculated to compare treatment conditions within and across studies. At posttreatment and follow-up, effect size and percentage responder data failed to clearly demonstrate an advantage or disadvantage of combined treatment over CBT alone for obsessive-compulsive disorder, social phobia, and generalized anxiety disorder. Some advantage of combined treatment over pharmacotherapy alone emerged from the few studies that allowed for such a direct comparison. In contrast, combined treatment for panic disorder seems to provide an advantage over CBT alone at posttreatment, but is associated with greater relapse after treatment discontinuation. The advantage of combined treatment may vary across the anxiety disorders. The potential differences in usefulness of combined treatment are discussed, directions for future research are suggested, and implications for clinical practice are considered.