Objective: The aim of this study was to assess the safety and effectiveness of paroxetine in a group of pediatric patients with obsessive-compulsive disorder (OCD) who had not previously been treated for that condition. Methods: In a 12-week, open-label study, 47 children (aged 9 to 15 years)were given a fixed dosage of paroxetine 20 mg/d for 6 weeks. During the next 6 weeks the treating psychiatrist could maintain or change the dosage based on therapeutic effectiveness or side effects. No additional medication was used. Scores on the Clinical Global Impressions-Severity of Illness (CGI-SI) scale, Maudsley Obsessive Compulsive Inventory (MOCI), Children's Depression Inventory (CDI), and Spielberger's State-Trait Anxiety Inventory for Children (SAI-C and TAI-C), were used to assess efficacy. Adverse effects were assessed by the Adverse Experience Scale and the CGI-Adverse Effect score. Results: The mean paroxetine dosage was 20.7 mg/d. Five patients dropped out of the study at week 6; 42 of 47 patients completed the trial and were assessed. At the end of 6 weeks the children were found to have significantly lower scores on MOCI (total) and the MOCI dirt, doubt, control, and slowness subscales and on the CGI-SI scale, CDI, SAI-C, and TAI-C. Twenty-six patients showed less than or equal to 50% improvement according to the MOCI. At the end of the study 12 children were classified as normal, 14 as borderline, and 11 as mild on the CGI-SI scale; all the patients were classified as moderate to most severe at baseline. The mean reduction in the CGI-SI score was 56.8% +/- 19.4%. No patient experienced side effects severe enough to discontinue the drug. Sleepiness (23.4%,), increase in anger (8.5%), fatigue (8.5%), behavioral disinhibition (4.3%), gastrointestinal distress (4.3%), and increase in preexisting ties (4.3%) were the most common side effects. Conclusions: Paroxetine was effective in the treatment of OCD in this sample of Turkish children, and the incidence of adverse events was low.