We examined magnetic resonance (MR) scans of the heads of 8 patients with late onset psychosis and 8 aged controls. Although some patients had mild cognitive impairment, none had depression or a history or examination suggesting focal brain disease. Thus, all patients met DSM-III-R criteria for late-onset schizophrenia. All 8 patients showed significant leukoencephalopathy or vascular pathology on MR imaging, and temporoparietal and occipital lesions were especially prominent. Little such pathology was evident on control scans. We suggest that focal brain disease of vascular origin may be associated with late-onset psychosis, and that MR scanning of such cases may provide important clues to pathogenesis.