TRANSTENTORIAL herniation, a recognized complication of expanding supratentorial lesions, is often heralded clinically by impairment of consciousness and other changes in vital signs, culminating frequently in decerebration and death.1-4These latter clinical events have been ascribed to secondary hemorrhagic extravasations in the midbrain and pontine tegmentum within the distribution of the mesencephalic perforating arteries (Fig 1 and 2). The purposes of this analysis of a large autopsy population are: first, to discern which of the preceding supratentorial lesions may preferentially lead to secondary brain stem hemorrhage (2° BSH), and secondly, to assess in retrospect the influence of other factors, such as age and sex, upon the frequency of this secondary lesion. Patient Material The data presented in this paper derive from 199 cases of 2° BSH which were extracted from the 7,110 consecutive, completely autopsied cases in the records of the Institute of Pathology, Kings County Hospital Center,