The protein C system is essential in limiting the activation of coagulation in vivo. We report the case of a 45 year old man with portal vein thrombosis complicated by ruptured oesophageal varices. Low concentration of plasma protein C was found in the patient and subsequently in one brother with a history of venous thromboembolism, and also in one son and one nephew who were asymptomatic. Hereditary protein C deficiency should be considered in patients with portal hypertension due to portal vein thrombosis.