This paper describes 15 patients who had elevated IgG antibodies reactive with cardiolipin. Outstanding clinical features were: recurrent venous and/or arterial thrombosis--often extensive and severe--in 9 cases. Thrombocytopenia, in 11 cases and spontaneous recurrent fetal loss in 8 out of 10 females with marital life. In addition there were vasospastic/thrombotic features such as livedo reticularis, Raynaud's phenomenon and leg ulcers. Involvement of central and/or peripheral nervous system was present in 10 cases. Valvular heart disease was conspicuous, 10 out of 15 patients (66%) had organic lesions in both sides of the heart. There were also laboratory abnormalities such as prolonged partial thromboplastin time, false positive V.D.R.L., plasmatic anticoagulant activity and low incidence of antinuclear antibodies and rheumatoid factors. The clinical syndrome seems to be related to the presence of antibodies reactive with anionic phospholipids, although there is not formal proof of a direct cause effects relationship. Recognition of these distinct clinical entity is important, the use of simple anti aggregating agents like aspirine and careful anticoagulant therapy may modify the course of this newly recognized autoimmune condition.