This report describes a case of livedo reticularis associated with increased titres of anticardiolipin antibodies (aCL) in a patient with systemic lupus erythematosus. A 38-year-old woman presented with fever, malaise, arthritis and livedo reticularis in a severe form. Antibodies to native DNA and an increased level of aCL were found. A significant positive correlation exists between livedo reticularis and elevated serum antiphospholipid activity in patients with systemic lupus erythematosus. aCL are shown to play a possible pathogenetic role in thrombotic events. This suggests that thrombosis is the underlying cause of livedo in these patients. A biopsy performed in a patient at the site where livedo was most marked showed no evidence of thrombi. It is postulated that the mechanism of livedo in lupus patients with aCL consists of both thrombosis and dysfunction in the regulation of the tone of the peripheral vascular bed.