A 23-year-old woman with factor XIII deficiency was presented. The patient had no consanguinity, but familial traits were present. A bleeding tendency and poor wound healing had been noted in the patient since birth. She had hemangiomas in the leg and vulva (Klippel-Weber disease). Hematologic studies revealed platelet dysfunction, cryofibrinogenemia and mild chronic disseminated intravascular coagulation with prolonged PT and PTT, hypofibrinogenemia, a high turnover rate of 125I-fibrinogen and mild elevation of fibrinogen-fibrin degradation products, β-thromboglobulin and platelet factor 4. A decrease in clot retraction and a marked reduction in maximal amplitude of thrombelastogram were also found. The assay of the factor XIII level was 10% by the antiserum inhibition method, and the assay of subunits A and S were 16 and 29%, respectively, by the electroimmunoassay method. Transamidase activity of factor XIII was 26%. The level of factor XIII of her sister was low, similar to that of the patient. The concentration of cold-insoluble globulin in EDTA-plasma was 36.5 mg/dl.