Although tumors of the midbrain have been repeatedly described, the emphasis has invariably been placed on the clinical manifestations of such lesions. The tumors already recorded include many forms: A large number were in the nature of pineal growths; others had their origin in adjacent areas of the brain and only by contiguity and direct extension involved the midbrain. Globus and Silbert1 clarified the histologic characteristics of a large quota of tumors of the midbrain of a somewhat varied appearance by identifying them as pinealomas, establishing this unity on an embryologic basis. They set these neoplasms apart from other neuroectodermal tumors occurring in that region. Such tumors, with their primary site of origin in the midbrain, are few. Bailey and Cushing2 encountered 18 in the brain stem (pons and midbrain) in a total of over 1,000 gliomas. None of these was classified or described. Tooth,3 in a