We have examined the demographic, clinical, and laboratory predictors of the concomitant or subsequent occurrence of lupus nephritis among a cohort of patients with disease manifestations < 1 year diagnosed as systemic lupus erythematosus (SLE) either at entry (baseline) into the cohort or during the subsequent 5 years. Patients studied were from a larger cohort with either early defined or undifferentiated connective tissue diseases; of the possible 74 patients, data were adequate in 58, 44 with SLE at entry and 14 at followup. Demographic, clinical, and laboratory data were examined first by univariate and then by multivariate analyses for their ability to predict lupus nephritis., Thirty of the 54 patients developed lupus nephritis with proteinuria as its most common manifestation. In 25 of the 30, nephritis occurred within the first 2 years of disease. Among those with a renal biopsy, the most common finding was World Health Organization class IV. By univariate analysis, the following variables were found more frequently among those patients who developed lupus nephritis versus those who did not: Younger age, hypertension, anti-double-stranded deoxyribonucleic acid and baseline diagnosis of SLE. In the multivariate analysis, only SLE at baseline and hypertension were identified as predictors of nephritis, whereas the presence of nonvasculitic skin rashes were negatively associated., Lupus nephritis is an early event in the course of SLE. Antinuclear antibody negative patients and those with incomplete SLE are less likely to develop lupus nephritis. Concomitant hypertension is associated with an increased risk of nephritis. © 1995 by Williams and Wilkins.