During the last decades, different pharmacological and psychotherapeutic strategies have been used to treat patients with obsessive compulsive disorder (OCD). Drugs that inhibit the serotonin recapture and the cognitive behavior therapy, that includes the exposure with response prevention and cognitive strategies, have been the most efficient treatment so far. This study's aims are to compare group cognitive-behavior therapy and standard pharmacological treatment (SRIs) in a world real population, using broader inclusion criteria. DSM-IV diagnostic criteria for OCD will be used (APA, 1994) and patients will be interviewed with the following instruments: SCID-I and Y-BOCS. Inclusion criteria are: (1) OCD diagnosis, (2) YBOCS score ≥ 16 (for patients with both obsessions and compulsions) or ≥ 10 (for patients with only obsessions or compulsions), (3) informed consent to participate in this clinical trial. Exclusion criteria are: (1) patients with clinical or neurological diseases that may be worsen by the medications included in treatment protocol, (2) Current substance dependence, (3) Current psychotic symptoms, (4) Current suicide risk. Patients will be randomized in blocks of 12 and with stratification for the following parameters: current SSRI, age, sex and previous response to treatment. Rates of improvement will be based on the results of the YBOCS scores for obsessions and compulsions and on the results of the clinical global impression scale. Pos-treatment measures will be assessed by psychiatrists or psychologists not involved in the patients treatment that will be blind for the treatment being received by the patient. The patient will be considered responsive to treatment when he or she presents a reduction in YBOCS score ≥ 35% of the initial score and a CGI score of 1 (very much improved) or 2 (much improved). The results of this study will help us to identify better health politics planning to a heterogeneous OCD population. So, it will improve our knowledge about the efficacy of the first line treatments in a real world OCD population.