A reversible depressive syndrome was found to be a very frequent side effect in a series of 33 patients subjected to stereotaxic surgery for the correction of abnormal movements. The depression was rated according to clinical and to Rorschach test parameters. The syndrome correlated significantly with age, depression being more frequent in adolescence, and with the side of the stereotaxic lesion, depression being more frequent after left thalamotomies in righthanded patients. The first correlation is of practical relevance, since it would clearly be wise to perform surgery before adolescence. The second correlation is of speculative interest in that is suggest a hemispheric asymmetry in the mood regulation processes. The incidence of this side effect in patients with abnormal movements may be further explained by the peculiar features of these patients, who need to be studied thoroughly before surgery.