Seventeen children with IgA nephropathy were grouped according to the absence (group I, n = 10) or presence (group II, n = 7) of glomerular basement membrane (GBM) deposition of IgA to determine whether GBM deposition of IgA correlated with laboratory or pathologic data at diagnosis or clinical status at follow-up. Children in group II had significantly (p less than 0.01) more proteinuria at diagnosis than children in group I. The percentage of glomeruli demonstrating crescent formation was significantly (p less than 0.05) higher in group II biopsies. Chronic changes of fibrous crescents, segmental sclerosis, global obsolescence, tubular atrophy, and interstitial fibrosis were also significantly (p less than 0.001) more common in group II biopsies. After a mean follow-up period of 2 years, all children in group II have persistent proteinuria of more than 1 g/24 h, and 3 of 5 have renal insufficiency (2 require dialysis). In contrast, 2 of 9 group I children have proteinuria exceeding 1 g/24 h, and only 1 has renal insufficiency. We conclude that, as compared to children with IgA localized to the mesangium, children with IgA nephropathy and GBM deposition of IgA have a higher urinary protein excretion at the time of diagnosis, more severe histologic alterations including a greater percentage of glomeruli demonstrating crescent formation, more chronic changes of segmental or global sclerosis, tubular atrophy, and interstitial fibrosis. Such children usually have persistent proteinuria and are more likely to develop progressive renal disease.