Four cases, two infants and two adults, of extensive thrombosis of the intracranial venous sinuses are described. Infarction of the brain had occurred in three cases. The first two cases presented as diabetic coma. The third case has been included to represent primary puerperal cerebral venous thrombosis. Extensive venous sinus thrombosis was seen at post-mortem examination in the fourth case, an infant who died suddenly, but there was no cerebral infarction in this case.