• To assess whether computed tomographic findings are present at the onset of schizophrenia, we evaluated CT scans of 35 patients with first-episode schizophreniform disorder, 17 with chronic schizophrenia, 23 with affective disorders, 27 with other psychiatric disorders, and 26 controls. Both the schizophreniform and the chronic schizophrenic patients had significantly larger cerebral ventricles than did the other psychiatric or control subjects. Ventricular size in the patients with affective disorder was not significantly different than in any of the other groups. Twenty percent of the schizophreniform patients had enlarged ventricles, (ventricular-brain ratio, > 10). The only other subjects outside this limit were four chronic schizophrenic patients (24%). Five schizophreniform patients and three with affective disorder had evidence of mild cortical atrophy. The results suggest that, in some schizophrenic patients, ventricular enlargement and less frequently cortical atrophy predate the onset of psychoses and are not a result of psychiatric treatment.