Participants in this double-blind study will be randomly assigned to receive EX/RP, risperidone, or placebo in conjunction with their regular SRI medication. All participants will remain on their regular SRI at a stable dose. During the first 2 months of the study, participants assigned to EX/RP will attend therapy sessions twice per week. In EX/RP, participants will be exposed to feared objects or ideas, and will be encouraged not to carry out a compulsive response. Participants assigned to risperidone or placebo will meet with a psychiatrist once every 1 to 2 weeks. At the end of 8 weeks, all participants' OCD symptom severity will be assessed. During this time, participants who have responded to treatment will continue receiving the same treatment for an additional 24 weeks. Participants assigned to EX/RP will meet with a therapist no more than 15 times total, and participants receiving risperidone or placebo will meet with a psychiatrist once every 4 weeks. Outcomes will be reassessed at study completion.