A case of congenital factor V deficiency is reported. Despite this defect in blood coagulation, the patient had experienced recurrent thrombophlebitis and was referred to us because of deep venous thrombosis of the lower limbs associated with pulmonary embolism. Both functional and immunological assays documented a deficiency of factor V (12 and less than 10%, respectively). The available family members were investigated and the same defect was found in 2 brothers of the propositus, who also suffered from thrombotic diseases (recurrent thrombophlebitis and myocardial infarction). The propositus has been treated with long-term oral anticoagulant therapy, no hemorrhagic complications or thrombotic recurrences being recorded in 2 years' time.