Direct attack on a tumor which has arisen from the pineal body has in the great majority of cases resulted fatally. A number of instances of operative intervention for the removal of tumor projecting into the posterior part of the third ventricle have been reported, but on analyzing them it is not certain that complete removal of a tumor of true pineal origin has ever been accomplished prior to the cases reported in this paper. The pinealoma is probably the commonest tumor of the posterior part of the third ventricle. Even though differentiation of the various tumors found here can be made only by biopsy and the operative approach is the same in all, I am considering only the tumor of true pineal origin. A large cystic tumor was removed by Sachs1in 1926 from the region of the pineal gland, but its exact nature was not definitely determined.