A strong correlation exists between the presence of an in vitro plasma coagulation inhibitor, named lupus anticoagulant, and a clinical syndrome of recurrent arterial and venous thromboses, neurological abnormalities, repeated obstetrical complications, thrombocytopenia, a biologic false-positive serological test for syphilis, and a variety of rarer manifestations. This syndrome has predominantly been observed in patients with autoimmune diseases, but it may be of similar importance in association with monoclonal gammopathies. As an introduction to a detailed analysis of ten observations which will also be published in this journal, this article reviews the clinical findings, the proposed pathogenetic mechanisms and the approaches to management of the lupus anticoagulant associated syndrome.