Objective: There is evidence of variation in the prevalence of co-morbid obsessive-compulsive disorder in schizophrenia amongst ethnic groups. This study evaluated the lifetime prevalence and clinical characteristics of obsessive-compulsive disorder (OCD)/ obsessive-compulsive symptoms (OCS) in Afrikaner schizophrenic and schizoaffective disorder patients. Method: An ongoing genetic study of schizophrenia is currently being conducted on the Afrikaner founder population. In this cohort of 400 subjects from the original genetic study, we identified 53 subjects with schizophrenia or schizoaffective disorder and co-morbid OCD/OCS (study group). They were matched for gender and age of onset of illness with 59 subjects who do not have OCD/OCS (control group). The diagnostic instrument used in this cohort is the Diagnostic Interview for Genetic Studies (DIGS) version 2, which has been translated into Afrikaans. In addition to the DIGS, information for the relevant clinical characteristics reported in this study was also drawn from a detailed narrative chronological summary report and clinical files. A checklist was completed. Results: The prevalence of co-morbid OCD/OCS amongst 400 subjects with schizophrenia or schizoaffective disorder was 13.2% [n=53] of which 40 were male and 13 female patients. The prevalence of OCD was 10.7% and OCS was 2.5%. Contamination obsessions [n=17] were the most common type of obsession reported, followed by religious obsessions [n=8]. The most prevalent compulsions were repetitive rituals [n=32] followed by checking behaviour [n=22]. Onset of psychotic symptoms was found to be insidious in 86.8% of the study group compared to 24.6% of the control group (p<0.0001). Second-generation antipsychotic use was found to be statistically more prevalent in the study group (77.4%), compared to the control group (45.8%) (p=0.0008). 73% of the study group experienced depressive symptoms compared to 50.8% of the control group. Both groups were found to have a similar incidence of suicidal thoughts and suicide attempts. Substance abuse amongst the control group was significantly higher (35.9%) compared to the study group (19.2%) (p <0.05). Cannabis was most commonly abused in both groups, followed by alcohol. Conclusion: The prevalence rate of 13.2% of co-morbid OCD/OCS in Afrikaner schizophrenia and schizoaffective disorder patients differs from findings in other ethnic groups, suggesting the possible role of genetic and cultural factors in the prevalence of co-morbid OCD/OCS. Second-generation antipsychotic use amongst schizophrenia and schizoaffective disorder patients with co-morbid OCD/OCS was found to be significantly higher than in those without co-morbid OCD/OCS. Clinical characteristics of Afrikaner schizophrenics and schizoaffective disorder patients with and without co-morbid OCD/OCS are the same, both groups were associated with significant psychopathology and a poor prognosis. phenomena in schizophrenia at between 3-59.2%. 4 This is considerably higher than the rate of 2-3% of OCD...