Plasma protein C exerts anticoagulatory effects by inactivating factors V and VIII. Hereditary protein C deficiency is transmitted as an autosomal dominant disorder. Homozygous individuals usually develop purpura fulminans as newborns; heterozygous protein C-deficient individuals are at increased risk for venous thrombosis and pulmonary embolism. However, arterial thrombosis has been only rarely observed. We describe a young patient with heterozygous protein C deficiency who experienced a severe stroke due to thrombotic occlusion of the left middle cerebral artery.