A retrospective clinicopathological study of 66 patients with IgA nephropathy was undertaken to determine the prognostic significance of various renal histopathological alterations and clinical parameters. At the latest follow-up, after a period of 60 to 72 months following biopsy, 18 patients had serum creatinine concentration above 1.8 mg/dl. When the entire patients were evaluated as a whole, the extents of interstitial broadening and glomerular sclerosis were correlated significantly with the final status of renal function: proteinuria of more than 1.0 g per day and mildly impaired renal function at the time of biopsy were also associated with unfavourable outcome. However, when the patients with initially normal renal function, i.e. serum creatinine level below 1.2 mg/dl, were evaluated separately, the initial amount of proteinuria, but none of the other parameters, had a prognostic significance in the subsequent course of renal function. These findings suggest that proteinuria of more than 1.0 g per day as an early event often indicates the progression of IgA nephropathy, and lead to a postulation that renal histopathological changes become more significant prognostic indicators in the relatively advanced stage of the disease.