The presence of focal signal hyperintensities on MRI images of the brain was compared in 48 schizophrenic patients, 26 patients with bipolar disorder and 34 healthy controls. Significantly larger areas of brain were affected by focal signal hyperintensities, particularly in the frontal lobes, in the schizophrenic group compared to the bipolar group and the controls. Although the bipolar group had more such foci than controls, this difference did not reach statistical significance.