In continuation of our previous studies on orbitofrontal cortex function in obsessive compulsive disorder (OCD) we studied a group of OCD patients with schizophrenia in comparison with a group of schizophrenia patients. In order to test orbitofrontal cortex function we again used an alternation learning task. We found no difference between the two groups in the performance of this task. The relationship between severity of OC symptoms and alternation learning was curvilinear. Thus, in the low range of symptom severity the correlation between alternation learning and symptom severity was negative, while in the high range it was positive. The positive correlation in the severely affected patients is essentially the same as that found in severe "pure" OCD patients, which we have previously reported. We conclude that the data indicate independent orbitofrontal cortex function in OCD, irrespective of comorbidity.