The occurrence of secondary brain stem hemorrhage was studied in 435 autopsies from patients with recent cerebral hemorrhage, infarction or ruptured cerebral aneurysms. The frequency of secondary brain stem hemorrhage was found to be 45% in cerebral hemorrhage, 15% in cerebral infarction, and 36% in ruptured aneurysms. In the majority of cases the secondary brain stem hemorrhage occurred a few days after the onset of cerebral hemorrhage or infarction. Ruptured aneurysms showed a more widespread temporal distribution of secondary brain stem hemorrhage. The median survival time was 2 days in cases of cerebral hemorrhage, 4 days in ruptured aneurysm and 4 days in cerebral infarction. The frequency of secondary brain stem hemorrhage was significantly lower in patients younger than 20 years. No significant difference was found in its distribution between the sexes. Secondary occipital lobe infarction was present in 3.5% of the patients. It is concluded that secondary brain stem hemorrhage is a common major contribution to the cause of death in stroke.