Cavum septi pellucidi (CSP) is a midline developmental anomaly shown to have increased incidence in patients with schizophrenia. The etiology of CSP may involve dysgenesis of the temporal lobes. This study evaluated the pattern of brain changes in three groups: 1) normal control subjects, 2) schizophrenic subjects without large CSP, and 3) schizophrenic subjects with large CSP. Patients without large CSP had decreased total brain, frontal, and temporal lobe volumes; patients with the anomaly had more pronounced right > left asymmetry and volume decrement limited to the left temporal lobe. These findings indicate that patients with schizophrenia and large CSP may show a different pattern of disturbed brain morphology than patients without this abnormality.