Explore the efficacy of methylphenidate hydrochloride controlled-release tablets add-on pharmacotherapy on clinical symptomatology and cognitive functioning in a sample of patients with obsessive-compulsive disorder (OCD) receiving fluvoxamine maleate. To test the hypothesis that methylphenidate hydrochloride controlled-release tablets augmentation of fluvoxamine treatment is well tolerated and may be proposed as an effective therapeutic strategy to improve outcome in OCD.