Nephritis developed in 230 of 609 private patients with systemic lupus erythematosus (SLE) (38 percent) followed up from 1950 to 1980. Eighty-seven percent of patients with nephritis were female; 71 percent were Caucasian. They were observed a mean of 10 years. Five- and 10-year survival rates were 80 percent and 65 percent, with improvement to 86 percent and 76 percent in the last decade. Normalization of urinary sediment and protein levels, blood pressure and serum albumin levels correlated with improved survival and tended to occur during the first year. Life-threatening complications of SLE were more common after the onset of nephritis but decreased as renal function worsened. Infection was the most frequent cause of death in the last decade. Forty-four patients received nitrogen mustard; 55 percent of the courses were followed by significant improvement in renal function and reduced steroid dosage. Control of the disease was associated with improved long-term survival of patients with SLE.