The antiphospholipid syndrome, initially described in systemic lupus erythematosus (SLE), occurs in 20-35% of patients with this condition. Its clinical manifestations may precede, be concurrent with, or follow clinical features of SLE. There are no major differences between the primary antiphospholipid syndrome and the secondary form that associates with SLE. Several studies suggest that the presence of an antiphospholipid syndrome in patients with SLE conveys a worse prognosis. To prevent recurrence of thrombotic events (particularly arterial events), oral anticoagulation with an international normalized ratio (INR) close to 3 is recommended. Treatment of recurrent fetal loss is with aspirin, or with aspirin plus heparin. Controlled studies are underway to determine optimal treatment in patients with cerebral ischaemia as well as the optimal treatment in women with recurrent pregnancy loss.