This study examined the effects of cognitive-behavior therapy (CBT) compared with traditional behavior therapy (exposure and response prevention [ERP]) in the group treatment of obsessive-compulsive disorder. Of the 76 participants who started treatment, 38 were wait-listed for 3 months before treatment to assess possible course effects. Both treatments were superior to the control condition in symptom reduction, with ERP being marginally more effective than CBT by end of treatment and again at 3-month follow-up. In terms of clinically significant improvement, treatment groups were equivalent on the conclusion of treatment, but 3 months later significantly more ERP participants met criteria for recovered status. Only 1 of 7 belief measures changed with treatment improvement, and the extent of this cognitive change was similar between CBT and ERP groups. Discussion includes consideration of optimal formats for the delivery of different types of treatment.