Characteristic ultrastructural alterations of the glomerular basement membrane (GBM) have been reported in hereditary nephritis. However, these GBM changes are not present in all patients with hereditary nephritis. In a retrospective study of 42 children with hereditary nephritis characteristic GBM changes were found in 28. The clinical features, renal biopsy findings and subsequent course were compared with those in the 14 without such changes. All 42 patients had hematuria. Eighty-two percent of the patients with the GBM changes showed progression of nephritis and 39% showed neurosensory deafness when last seen. In contrast, all patients without the GBM changes had a normal audiogram, ran a nonprogressive course and had hematuria only when last seen. Light microscopy of renal biopsy specimens revealed segmental glomerular sclerosis and interstitial foam cells only in patients with the GBM changes. Our study shows that the presence or absence of these GBM changes is the most reliable indicator of the prognosis in children with hereditary nephritis.