Introduction: Comorbid obsessive-compulsive disorder (OCD) has been reported among patients with schizophrenia in other countries. But, the literature is not well-documented on this issue in Iran (Persia). The present study aimed to investigate the prevalence and severity of OCD and some of its related factors in a group of patients with schizophrenia in Iran. 
Methods: This is a cross-sectional study. A total of 150 hospitalized patients with schizophrenia were recruited at Razi Psychiatric Hospital in Tehran, Iran. Demographic and clinical checklists, as well as the Yale-Brown obsessive-compulsive scale (Y-BOCS), scale for assessment of negative symptoms (SANS), and scale for assessment of positive symptoms (SAPS) were administered to collect data. OCD was the dependent variable and independent variables included age, sex, severity of positive and negative symptoms, duration of schizophrenic disorder, the number of hospitalizations, and antipsychotic medications administered to them. Data were analyzed by analysis of variance (ANOVA), Chi-square, and T-test. 
Results: Overall, 31.3% of patients had OCD with an average severity of 12.81(SD=10.27). The prevalence of OCD was not affected by the number of psychiatric hospitalizations for schizophrenia or the duration of schizophrenic disorder. The severity of OCD significantly reduced as the duration of schizophrenia and the severity of negative symptoms increased. 
Conclusion: OCD was found among a considerable proportion of the study sample. OCD may be associated with exacerbating schizophrenic symptoms. Therefore, psychiatrists should consider the simultaneous treatment of OCD and schizophrenia. Further studies are suggested in this issue.