The study was prompted by the suggestion that inflammatory polyarthritis and corticosteroids increase articular mobility. Ninety female patients with systemic lupus erythematosus (SLE) of whom 85 had polyarthritis and at least 75 of whom had received corticosteroid therapy were studied and compared to an equal number of carefully matched controls. The difference between the number of hypermobile patients [6 (7%)] and controls [5 (6%)] was not significant. There was also no significant difference when either the pooled mobility scores or the pooled hand scores of the patients and controls were compared. No significant association between articular mobility and either age at onset of disease, duration of disease or corticosteroid therapy was demonstrated. There was a significant association between deformity and duration of disease (p = 0.04) but not with mobility score. We conclude that SLE patients do not have a hypermobile tendency and therefore that neither SLE nor corticosteroids predispose to increased articular mobility. There is also no association between articular mobility and deformity.