The antiphospholipid or Hughes' syndrome is the association between antiphospholipid antibodies, recurrent venous and arterial thromboses and recurrent fetal loss. There are many clinical manifestations arising from this acquired thrombophilia and these are described in the article. The pathogenic mechanism by which the antibodies cause thrombosis is the subject of much debate, and current theories are described. The diagnosis and management of patients with the syndrome are also discussed.