Deep vein thrombophlebitis (DVT) and pulmonary emboli (PE) have been uncommonly reported manifestations of systemic lupus erythematosus (SLE). This may be partly due to their being masked by other more familiar lesions of the lungs and extremities in SLE. We have identified 17 patients with SLE from a population of 180 being followed up prospectively who had 21 attacks of DVT and/or PE. Of the total of 21 episodes the SLE was considered to be active in 14, inactive in 6, and variable in a patient with recurring phlebitis. The incidence of hyperlipidaemia, smoking history, and use of birth control medication or corticosteroids was not higher in these patients. These clinical findings thus constitute additional features of SLE occurring in about 9% of patients and may be significance for morbidity and mortality.