Pedigrees were obtained from 340 patients with systemic lupus erythematosus (SLE). Two hundred ten (62%) of the patients were from the wards of Lupus Clinic at the Los Angeles County-University of Southern California Medical Center, and 130 (38%) were from a private practice. Forty-one (12%) of the 340 patients with SLE had affected relatives: five had two and 36 had one affected relative. Ten (30%) of the 33 male patients and 31 (10%) of the 307 female patients had relatives with SLE. Examination of the individual pedigrees included examples of possible autosomal dominant, autosomal recessive, and sex-linked dominant and recessive inheritance. When all the pedigrees were considered as a group, multifactorial inheritance was suggested.