 Previous studies showed that approximately 33-50 of OCD patients who have not had an adequate response to SRI medication had a positive response when an atypical antipsychotic medication was added. However, the problematic acute and long-term side effects of these medications are of concern and, at times, limit their use. Paliperidone has a number of advantages over these medications including fewer drug interactions and better tolerability. Thus, this study is designed to determine whether paliperidone augmentation of an existing medication is effective relative to taking a placebo and your existing medication. 