 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 Bloch et al., 2006. Risperidone has been the most studied agent and has the most consistently positive findings e.g., McDougle et al., 2000. However, the problematic acute and long-term side effects of risperidone and other atypicals are of concern and, at times, limit their use. Paliperidone, a metabolite of risperidone that utilizes OROS osmotic drug-release technology, has a number of advantages over risperidone including a lack of drug x drug interactions and a predictable pharmacokinetic profile that is associated with better tolerability. Thus, paliperidone has the potential to be a safer alternative for augmentation in OCD patients pending supporting efficacy data. Given the need to examine the efficacy of paliperidone, this protocol is designed to determine whether paliperidone augmentation of an SRI is effective relative to a placebo-control, and safetolerable in patients with OCD who have not adequately responded to past adequate SRI treatment. 