Fifteen years have passed since Hughes reported the detailed clinical description of antiphospholipid syndrome (APS), and it is now recognised as one of the most common prothrombotic disorders. Its main clinical features are recurrent thrombosis (both venous and arterial), recurrent pregnancy loss and thrombocytopenia associated with the presence of antiphospholipid antibodies (aPLs). aPLs are a heterogeneous group of autoantibodies detected by either clotting or immunological assays. They include lupus anticoagulant (LA), anticardiolipin antibodies (aCL) and antibodies against other phospholipids (PLs). Recently the aPLs family has expanded to include antibodies whose specificity are claimed to be directed not only towards PLs, but also towards plasma proteins and their complex with PLs. Animal models are providing important new data on clinical and pathogenic aspects of APS. The detection of antibodies against beta 2 glycoprotein I by a simple and rapid enzyme-linked immunosorbent assay (ELISA) may facilitate the recognition of "pathogenic" aCL in APS. Regarding the treatment of APS, long-term anticoagulation therapy is needed to prevent recurrences.