IgA nephropathy (IgAN) may present with a wide variety of histologic patterns on renal biopsy, ranging from a minimal lesion to a diffuse proliferative glomerulonephritis (GN). The histologic features of 244 cases of IgAN (not including Schönlein-Hanoch nephritis) diagnosed between 1980 and 1994 were reviewed, and each case was subclassified using the following, relatively simple histologic classification scheme: subclass I (39 cases): minimal or no mesangial hypercellularity, without glomerular sclerosis; subclass II (18 cases): focal and segmental glomerular sclerosis without active cellular proliferation; subclass III (110 cases): focal proliferative GN; and subclass IV (42 cases): diffuse proliferative GN; and subclass V (35 cases): any biopsy showing > or = 40% globally sclerotic glomeruli and/or > or = 40% estimated cortical tubular atrophy or loss. Subsequent analysis of renal survival in 109 patients who underwent biopsy before or during 1992 for whom such data were available showed a strong, statistically significant correlation between histologic subclass and renal survival, with an order I, II (greatest survival) > III > IV, V. Crescents were a significant negative prognostic indicator for renal survival in subclass III (but not in subclass IV), and interstitial expansion was a negative prognostic indicator in subclasses III and IV, although the statistical significance of these were not maintained after controlling for serum creatinine at the time of biopsy. The presence of peripheral glomerular capillary deposits ultrastructurally had no prognostic significance. With respect to clinical presentation, hypertension (systolic blood pressure > or = 130 mm Hg and diastolic blood pressure > or = 90 mm Hg) and proteinuria of > or = 2.0 g/24 hr were significant negative prognostic indicators for renal survival, even when controlling for serum creatinine at the time of renal biopsy. The presence of gross hematuria correlated significantly with increased renal survival by univariate analysis, but not when controlling for serum creatinine at the time of renal biopsy. The findings of this study confirm the wide variety of clinical and histopathologic presentations of IgAN, and indicate the utility of the proposed histologic classification schema in assessing a patient's likelihood of ultimately developing end-stage renal disease.