Magnetic resonance imaging (MRI) was performed in 12 patients with schizotypal personality disorder (SPD), 11 patients with chronic schizophrenia, and 23 age- and sex-matched normal volunteers. MRI slices were acquired in the axial plane at 1.2-mm intervals, and the ventricles were traced on every other slice. The lateral ventricular system was divided into the anterior horn, temporal horn, and dorsal lateral ventricle. Schizophrenic patients had larger left anterior and temporal horns than the normal volunteers. Size of the left anterior and temporal horn in SPD patients was intermediate between those of normal volunteers and schizophrenic patients and differed significantly from schizophrenic patients. The left-minus-right difference was larger in schizophrenic patients than in normal volunteers or SPD patients. Thus, in their structural brain characteristics, as well as in their clinical symptomatology, SPD patients evidence, in attenuated form, abnormalities resembling those found in full-fledged schizophrenia. The findings suggest that decreased left hemispheric volume, in frontal and temporal regions, may characterize both psychotic and non-psychotic disorders of the schizophrenia spectrum.