Obsessive-compulsive-related disorders are frequently comorbid with schizophrenia. The existence of obsessive and compulsive symptoms in patients with schizophrenia represents one of the most severe types of psychotic disorders and may predict a poor prognosis in most cases. Previous pilot studies and case reports have shown that the condition of some patients with schizophrenia did not exacerbate and even improved when serotonin reuptake inhibitors (SSRIs) were added to their standard neuroleptic regimen. The aim of this study was to evaluate the efficacy of a combination treatment of an SSRI (fluvoxamine) and standard neuroleptics for the treatment of obsessive-compulsive (OC) symptomatology in patients with schizophrenia compared with administration of neuroleptics only. Thirty inpatients who met DSM-IV criteria for schizophrenia and also had prominent OC symptoms were randomly divided into two groups. Fourteen patients were treated with conventional neuroleptics and fluvoxamine in doses of 100 to 200 mg/day for 8 weeks. Sixteen patients comprised a control group and received only their previous therapeutic neuroleptic therapy. The patients were assessed using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), the Positive and Negative Syndrome Scale (PANSS), and the Clinical Global Impression Scale (CGI) at baseline and endpoint. Side effects were assessed weekly. The data were analyzed using an analysis of variance. A considerable reduction in PANSS (34.3%) and Y-BOCS (29.4%) scores was noted, and CGI scores decreased moderately in both groups. None of the patients showed an acute exacerbation at the end of the study. Side effects were mild and easily tolerated in most patients. This open, randomized, controlled study reveals that coadministration of fluvoxamine, an SSRI, and neuroleptics in patients with schizophrenia and OC symptoms was associated with specific improvements of these symptoms. Thus, the use of an SSRI in treating a patient with schizophrenia and OC symptomatology may be warranted and safe. Other implications of the findings, including general safety of the combined pharmacotherapy and the use of new antipsychotic medications, are also discussed.