Renal prognosis cannot be easily predicted in females with hereditary nephritis (HN). Thirty-six women with persistent urinary abnormalities, belonging to 24 families with progressive HN, were studied. Renal biopsy specimens were available in 23 patients and were studied by light and electron microscopy (EM). Nine women (group I) progressed to early renal failure, at 35 yrs of age or less. Five women (group II) progressed to late renal failure at 45 yrs of age or more. In contrast, 22 patients have so far normal renal function, and 14 of these (group IV) range from 31 to 62 yrs of age. Diffuse glomerular basement membrane (GBM) thickening was found by EM in 6 of 7 cases of group I, whereas it was found in no patient of group IV. The following features are suggestive of progressive nephritis in females: gross hematuria in childhood, nephrotic syndrome, and diffuse GBM thickening by EM. In contrast, family history of HN without nerve deafness, normal or nearly normal kidney on repeat biopsy, and thin or normal GBM by EM are suggestive of less or nonprogressive renal disease. Further follow-up is needed to assess the prognostic significance of these features.