Twenty-three chronic schizophrenic patients and 23 controls, all males between 20 and 40 years of age, were evaluated by CT scan. The lateral, third and fourth ventricles, the Sylvian fissures, and the largest sulcus from each of the frontal, parietal, and occipital lobes, were measured in order to determine whether the previously reported ventriculomegaly in schizophrenics was perhaps due to a disturbance of CSF flow or to atrophy, two common causes of ventricular enlargement. We found that in the schizophrenic group the third and fourth ventricles and both Sylvian fissures were significantly enlarged, but not the lateral ventricles or cerebral sulci. Our data suggest that these ventricular changes are not due to a disturbance of CSF flow or to cerebral atrophy. Other possible explanations are discussed.