The purpose of the present study was to investigate the changes in the cognitive dysfunctions of patients with obsessive-compulsive disorder (OCD) over a 1-year period of pharmacological treatment. Twenty-one OCD patients and 20 normal subjects underwent neuropsychological tests and clinical evaluations on three separate occasions (baseline, 4 months, and 1 year after the start of medications). OCD patients continued to show significant impairments in the following cognitive measures compared with the normal controls: accuracy of immediate and delayed recall on the Rey-Osterrieth complex figure tests, the numbers of responses on the category fluency test, the response time on the trail making test--part A, and the number of perseverative response and perseverative errors on the Wisconsin card sorting test. The findings in this study suggested that impaired performance on cognitive domains, such as visuospatial memory and verbal fluency may underline the pathology of OCD.