Two patients with angiographically proven longitudinal sinus thrombosis were studied from a coagulation point of view. In the first case, marked primary thrombocytosis was found. This patient was treated with aspirin, dipyridamole and radioactive phosphorus. In the second case, fibrinogen and whole blood plasma viscosity were elevated. This patient developed deep vein thrombosis of the left leg a few weeks after the cerebral episode and was treated with coumarin drugs. The importance of a coagulation study in every patient with cerebral vein thrombosis is emphasized.