The independent predictors of progression of IgA nephropathy (IgAN) were investigated by multivariate life table analysis, using Cox's proportional hazard model, in 225 patients with IgAN diagnosed by renal biopsy (Bx). There were 105 men and 120 women. Mean age at Bx was 32.5 years. The follow-up period following Bx was 4.0 +/- 2.6 yrs, ranging from 5 months to 11 yrs. The clinical parameters analyzed were age at the time of discovery of the disease, age at Bx, intervals from discovery to Bx, presence or absence of macrohematuria, and clinical data at Bx such as presence or absence of hypertension, the degree of hematuria, the amount of urinary protein excretion, serum creatinine and serum IgA concentration. The following immunopathological parameters were also examined; glomerular hypercellularity index, percentage of glomeruli associated with segmental lesions such as tuft adhesions, crescents and segmental sclerosis, percentage of obliterated glomeruli by global sclerosis, severity of interstitial infiltration, fibrosis, arterial wall thickening, arterial hyaline changes, and intensity of the depositions of IgG, IgA, IgM, C3, C1q and fibrinogen by immunofluorescent study. Among all clinical and pathologic parameters examined, the following parameters were proved to be significant independent predictors of progression of IgAN: serum creatinine exceeding 1.5 mg/dl in men and 1.3 mg/dl in women, proteinuria over 2 g/day, segmental lesions involving more than 25% of glomeruli and interstitial fibrosis occupying more than 25% of cortical area.(ABSTRACT TRUNCATED AT 250 WORDS)