Circulating anticoagulants directed against factor VIII coagulant activity are very rarely encountered. Eighteen per cent of them have been described in the peripartum period of primiparae aged 28 years on average. The clinical signs are the same as those of constitutional haemophilia, but they differ in frequency. The most common of these signs are haematoma, ecchymoses and haematuria. The diagnosis is confirmed by prolongation of clotting time alone, presence of an anticoagulant in blood and specific assay of the deficient coagulant factor. These inhibitors are usually immunoglobulins of the IgG type. The cause and pathogenesis of the disease are unknown. Treatment consists of administering coagulant factors in haemorrhagic periods and immuno-suppressive therapy. Spontaneous remissions are frequent.