To clarify the risk factors for chronic renal failure in idiopathic IgA glomerulonephritis (IgA-GN), we performed a dual study on 282 patients using both standard univariate statistical methods and the multivariate regression model of Cox. During a follow-up ranging from 1 to 36 years, with a mean of 8 years, 18% of the patients (50/282) had gone into chronic renal failure (CRF), with 18 of them in end-stage renal disease (ESRD) (6%). The univariate comparison of patients with CRF versus patients without CRF showed multiple risk factors: mainly arterial hypertension, an amount of proteinuria, nephrotic syndrome, a high level of serum IgA, presence of HLA-B35 antigen, and the intensity of most pathological lesions on light microscopy. The actuarial survival rate for a normal renal function (serum creatinine less than 135 mumol/L [1.5 mg/dL]) was 84% at 10 years and 64% at 20 years. The multivariate study allowed the isolation of only four risk factors with a significant effect on survival rate. These were the amount of proteinuria, the global optical score on first renal biopsy, the presence of an initial hypertension, and the presence of the HLA-B35 antigen. From these results, the probability of renal survival for individual patients may be calculated and a high-risk subgroup defined. Our data confirm the greater usefulness of multivariate over univariate statistical analyses in finding risk factors for CRF in IgA-GN.