The clinical course and outcome of 91 children less than 15 years of age at onset and followed for at least 1 year have been retrospectively analyzed. The course has been characterized by recurrent macroscopic hematuria in 74 patients, by proteinuria-microscopic hematuria and a single episode of macroscopic hematuria occurring either at onset or a few months later in 8, by proteinuria-microscopic hematuria in 7, and by proteinuria only in 1. Lastly, one patient showed rapidly progressive renal failure. Four groups were identified by light microscopy: minimal glomerular changes (26), focal and segmental glomerulonephritis (41), pure mesangial proliferation (3) and proliferative glomerulonephritis with crescents (21). A good correlation was found between the glomerular lesions observed by light microscopy and the outcome. In this series we have not observed a dramatic clinical deterioration suggesting a transformation from one histologic type to another, as reported by others. None of the 70 patients belonging to the first three groups has impaired renal function but two with focal and segmental glomerulonephritis have developed hypertension. Although the clinical course is benign, many patients have, at the last observation, an abnormal urinalysis characterized by microscopic hematuria and/or mild proteinuria; the proteinuria is over 1 g/24 h in six patients with focal and segmental glomerulonephritis. Ten patients remained in clinical remission for several years, but mesangial IgA deposits were still present in the only patient who had a repeat biopsy while in remission. In contrast, none of the patients with proliferative glomerulonephritis with crescents has had a prolonged remission. Six patients developed terminal renal failure 0.7, 0.11, 2, 4, 8 and 10 years after onset. Two additional patients are in moderate chronic renal failure with hypertension 10 and 12 years after onset. Most children show a persistent nephropathy, (in five proteinuria is over 1 g/24 h), and two of them have developed hypertension. Therapeutic trials using drugs with side-effects should, therefore, be used only in this group of patients.