Previous studies of long-term serial changes in ventricular size in schizophrenia (SCZ) have yielded mixed, albeit predominantly negative results. The current study examined ventricular changes in CT scans over intervals of 1-to 4 1/2 years in chronic schizophrenic and bipolar patients. The results indicated significant progression of ventricular size from initial to final scan in the schizophrenia group but not in the bipolar or control groups; the percent increase in VBR over baseline was 25% (p less than 0.01) in the schizophrenia group as compared with 11% (n.s.) in the bipolar group. The increases in ventricular enlargement in the schizophrenic group did not correlate with duration of illness but did appear to show an irregular stepwise pattern in several patients. It is concluded that progressive ventricular enlargement after onset of illness does occur in a subgroup of schizophrenic patients characterized by a chronic or deteriorating clinical course. The etiological implications of this finding are discussed.