OBJECTIVE Although deforming arthropathy in systemic lupus erythematosus (SLE) is characterised by a number of manifestations, definitive criteria for the different forms have not yet been established. To define deforming arthropathy and its different types a study was undertaken of 176 SLE patients. METHODS Using as criterion any deviation from any of the metacarpus finger axes 17 patients (16 women, one man) were identified with clinical deforming arthropathy. These patients were evaluated according to a standardised protocol that covered all known characteristics of deforming arthropathy. By means of "Jaccoud's arthropathy index" three different forms were identified. RESULTS Three patients had an erosive form of deforming arthropathy (or rhupus hand) such as those seen in frank rheumatoid arthritis (RA), eight patients were identified as having Jaccoud's arthropathy (or lupus hand), and the remaining six patients had mild deforming arthropathy. Jaccoud's arthropathy is characterised by severe deformation of the hands (ulnar deviation, swan neck deformities, and Z deformity of the thumb) and feet with multiple non-erosive subluxations, mild aching and little or no evidence of synovitis. All patients, but one, fulfilled just four criteria of the ACR classification and joint symptoms were always found to precede the diagnosis of SLE. Furthermore a remarkable association of Jaccoud's arthropathy with fetal loss, thrombosis--both venous and arterial--and the presence of antiphospholipid antibodies was found. CONCLUSIONS These data suggest that Jaccoud's arthropathy represents a subset of SLE. Subdivision of deforming arthropathy into several clinical forms can facilitate the clinical management of this disorder.