In a retrospective study, brain magnetic resonance images of 12 patients with the onset of manic symptoms after the age of 50 years were compared to age- and sex-matched control subjects for the incidence, size, and location of subcortical hyperintensities. Compared with controls, the patients demonstrated a significantly greater number of large subcortical hyperintensities, particularly in the middle third of the brain parenchyma. The lesions occurred with equal frequency in the right and left hemisphere. There were no differences between the two groups in the size of the ventricles or the presence of periventricular hyperintensities.