PONTINE hemorrhage frequently has been noted at necropsy in cases of supratentorial tumor. This has not been an uncommon finding at the Mayo Clinic during the last five years, but prior to 1940 pontine hemorrhage rarely was noted at necropsy in cases of tumor of the brain. This study of vascular lesions of the brain stem was undertaken to aid in the clinical recognition of such lesions in the presence of other intracranial lesions and to investigate the possible mechanisms causing the hemorrhage. In 1903, Dana1reported the results of a study of lesions of the brain stem. He said that pontine hemorrhage was rather rare and that it accounted for 1 to 10% of all intracranial hemorrhages. Attwater,2in 1911, in a review of 67 cases of pontine hemorrhage which had been observed at Guy's Hospital in the previous 36 years, found that necropsy disclosed a small