The authors undertook a case-control study to explore the many factors that have been postulated to be related to the etiology of systemic lupus erythematosus. A total of 195 cases of systemic lupus diagnosed in the Philadelphia, Pennsylvania, metropolitan area between 1985 and 1987 were compared with 143 controls, friends of the cases matched to them according to age (+/- 5 years) and sex. Through personal interviews and chart reviews, data were collected on demographic factors, personal and familial medical history, reproductive history, medication history, and environmental exposures. Associations were found between systemic lupus erythematosus and having a family history of autoimmune disease (age-, sex-, and race-adjusted odds ratio (OR) = 2.3, 95% confidence interval (CI) 1.2-4.6), a history of shingles (adjusted OR = 6.4, 95% CI 1.4-28.0), a history of hives (adjusted OR = 1.8, 95% CI 1.1-3.0), and a history of medication allergies (adjusted OR = 2.6, 95% CI 1.5-4.5). No association was present between systemic lupus erythematosus and either any use or recent use of oral contraceptives (e.g., OR = 0.6 (95% CI 0.2-1.4) for use in the 3 years prior to diagnosis), family history of multiple other diseases, or a history of numerous other infections or various other types of allergies. Thus, these data indicate that systemic lupus erythematosus is associated with a family history of autoimmune diseases, a history of shingles, and a history of allergies. In contrast, if the development of systemic lupus is affected by use of oral contraceptives, this effect must be extremely modest. These findings may help clarify the possible pathogenesis of systemic lupus erythematosus, and they provide clues as to when the presence of systemic lupus should be suspected.