Unusual nail changes have been observed in 42 of 165 patients with systemic lupus erythematosus (SLE) followed at the Wellesley Hospital, Toronto, Canada, over the past seven years. These changes had almost the same frequency as mucous membrane ulcerations seen in 31% of the patients. Nail changes were associated with active disease in 39 of the 42 patients. Patients with nail changes had a significantly higher incidence of Raynaud's phenomenon and mucous membrane ulcerations than patients without these changes. There was no increased incidence of other skin manifestations or of systemic vasculitis in these patients. Thus, nail changes may be an additional helpful criterion in the diagnosis of SLE.