Prevalence of lupus anticoagulant (LA) in patients with systemic lupus erythematosus (SLE) and clinical manifestations vary widely between different clinical series. We investigated the relation between LA, autoimmune hemolytic anemia (AIHA), thrombocytopenia and platelet dysfunction in 80 unselected patients with SLE. AIHA was found in 6 patients (7.5%) and thrombocytopenia in 10 patients (12.5%), which was not related to platelet aggregation abnormalities. Compared to controls, patients with SLE showed significantly prolonged aPTT and kaolin clotting time (KCT), but platelet aggregation induced by both collagen and thrombin was not impaired. LA activity as defined by Rosner et al. (index for LA/ICA) was found in 15 patients (18.9%). Only 7 of these patients showed a positive platelet neutralization test (Triplett) and 9a positive tissue thromboplastin inhibition test (Schleider). In our SLE patients 23.7% have suffered from at least one thrombotic complication. In patients with LA activity thromboembolic complications were increased (p0.05). Thrombocytopenia was found in 6% of LA-negative but in 20% of LA-positive patients.