Antiphospholipid syndrome (APS), first described and termed in the early 1980's, is defined by its clinical and laboratory signs. If other disorders inducing antibody production are excluded, APS may be considered a primary disease. Or it can be a secondary condition that is usually seen in systemic diseases of connective tissues. The main concept of APS is based on strong association between its clinical and laboratory manifestations and patient's medical history. Clinical signs include recurrent arterial and venous thrombosis or repeated fetal losses; laboratory criteria involve lupus anticoagulant (LA) syndrome or medium and high titres of anticardiolipin (aCL) antibodies. Thus defined, APS represents the most common form of acquired thrombophilic conditions while the basic concept lies in strong association between specific clinical manifestations and repeated detection of LA or aCL. Antiphospholipid antibodies (LA and aCL) are extremely heterogeneous antibody groups whose effect on processes at different levels of coagulation cascade varies. Their effect can be analogical to the action of phospholipid surfaces at various points of blood coagulation. This process usually results in development of a certain degree of thrombophilia. Present level of understanding of APS indicates that characteristics of clinical signs and detection and evaluation of antiphospholipid antibodies have not been definitely established yet and are to be specified with the help of molecular geneticists, immunologists, biochemists, hematologists and rheumatologists.