Protein C deficiency has been reported to be associated with a high risk for thromboembolism. We report three patients with protein C deficiency: one suffered from left renal vein thrombosis, another from recurrent venous thrombosis of the legs complicated by pulmonary embolism and the third from an extensive thrombosis of the splanchnic veins with partial Budd-Chiari syndrome. We discuss the unusual sites of venous thrombosis in protein C deficient patients, the factors which may act as thrombotic trigger and the strategy of long-term prevention.