Renal insufficiency is one of the most severe outcomes of systemic lupus erythematosus (SLE). The aim of this study was to identify baseline predictors of the development of renal insufficiency in a cohort of patients with SLE. 281 patients from the The Hopkins Lupus Cohort (HLC) enrolled between 1987-1994 were followed for the occurrence of renal insufficiency, defined as a serum creatinine 1.6 mg/dl for men and 1.4 mg/dl for women. Over a mean (+/-s.d.) of 3. 3+/-2.1 y of follow up, 46 (16%) of the 281 patients developed renal insufficiency. Using a multivariate Cox proportional hazard model, we found the risk of renal insufficiency associated with younger (0-19 y) or older (40 y) age at baseline (relative risk (95% CI) 5.1 (1.4, 18.8) and 4.1 (2.1, 8.2)) and longer duration of SLE before referral to the cohort (RR 1.25 [1.05, 1.5] for every five years). Additional predictive variables were borderline elevation of serum creatinine at baseline (RR 3.1 (1.4, 6.6) for a serum creatinine 1. 4-1.5 mg/dl for men and 1.2-1.3 mg/dl for women), and mean proteinuria (RR 3.6 (1.8, 7.4) for trace-3+ and 10.6 (3.8, 30.0) for 3+ (urine dipstick level)). Socioeconomic status, race, autoantibodies and complement were not significantly associated with the risk of renal insufficiency. This study supports early referral of SLE patients to rheumatologists and emphasizes the importance of early signs of renal involvement as predictors of later renal insufficiency in SLE patients.