The purpose of this study was to investigate whether the presence of anticardiolipin antibodies (aCL) in systemic lupus erythematosus (SLE) patients was associated with particular laboratory or clinical features. Anticardiolipin antibodies were determined in 63 unselected SLE patients: 32 (50.8%) were found to be aCL positive and this positivity was significantly associated with the presence of lupus anticoagulant (p less than 0.003) and false positive VDRL reaction (p less than 0.001), but not with other haematological or biological markers. Thrombin-antithrombin III (TAT) complexes were found to be increased with disease activity, but no relationship was found between TAT complexes and the presence or absence of aCL. In this study a statistically significant association was found between aCL positivity and arterial thromboembolic events, but not with venous thrombotic complications. In summary half of SLE patients had aCL and the presence of these antibodies was associated with other antiphospholipid antibodies and with arterial thromboembolic events.