ABSTRACT Objective: To document the prevalence of obsessive-compulsive disorders (OCD) among patients admitted at Mathari Psychiatric Hospital, Nairobi, Kenya. Method: This was a descriptive cross-sectional study conducted at the Mathari Hospital. Results: Out of 691 patients interviewed, 84 (12.2%) had symptoms which met the Diagnostic and Statistical Manual of Mental Disorders (DSMIV) criteria for OCD, which started early in life. The clinicians had not recognized the OC symptoms/disorder. There were high co-morbidities between OCD and other Structured Clinical Interview for DSM-IV (SCID) core syndromes as well as psychotic symptoms often associated with schizophrenia. Conclusion: OC symptoms are common in psychiatric patients admitted at Mathari Hospital although such symptoms were clinically undetected and therefore not managed. The high co-morbidities between OCD, other psychiatric disorders and other psychiatric symptoms pose clinical challenges in differentiating between psychotic symptoms perceived by the patients to have an external locus and OC symptoms perceived to have an internal locus. A more systematic clinical procedure for assessing all DSM-IV symptoms should be adapted as standard quality control practice in all patients, particularly those with psychotic symptoms.