The authors studied mortality among 2513 relatives of 56 Japanese patients with systemic lupus erythematosus. The observed deaths in 142 relatives were compared with the expected number of deaths. The observed number of deaths was significantly less among relatives of patients with systemic lupus erythematosus (p less than 0.01). Deaths from malignant neoplasms and senility (senescence) were significantly lower than the expected number of deaths among relatives (p less than 0.05).