Ninety-three patients with acute stroke lesions restricted to the right hemisphere were examined for the presence of mood changes. While 46 patients showed no mood changes, 19 were unduly cheerful, 17 had developed major depression, and 11 had developed minor depression. Although there were no significant between-groups differences in other demographic variables, neurological deficits, activities of daily living, cognitive impairment, or quality of social support, patients with major depression had a significantly higher frequency of familial history of psychiatric disorder and lesions of the parietal cortex than patients with either no mood change or major depression following left-hemisphere lesions. On the other hand, undue cheerfulness was significantly associated with lesions of the right frontal operculum. These findings suggest that major depression following right-hemisphere lesions may have a different aetiology and mechanism than major depression following left frontal or basal ganglia lesions.