Lamination of the basement membrane has been considered to be the lesion characteristic of familial nephritis and attenuation to be the lesion of "Benign" familial hematuria. Electron micrographs were reviewed of 57 children who had renal biopsies for persistent hematuria. Attenuation or lamination of the glomerular capillary basement membrane was found in each. Twenty of the 57 children had familial nephritis; 20 had familial hematuria; and 17 had no involved relatives. Follow-up data were available for 14 of 20 children with familial nephritis, 12 of 20 with familial hematuria, and 12 of 17 with sporadic hematuria for 13.6 +/- 6.3, 6.7 +/- 4.6, and 7.0 +/- 4.8 years, respectively, after discovery of hematuria. Five children developed end-stage renal disease: three with familial nephritis, one with familial hematuria, and one with sporadic hematuria. Only two no longer had hematuria. Attenuation of the glomerular capillary basement membrane was seen in every biopsy, whereas lamination was not. Because hematuria and ultrastructural abnormalities were findings shared by all the children, we suggest the possibility that familial nephritis, and familial or sporadic hematuria as defined in this study, may be variations in a spectrum of inherited abnormality or abnormalities in the formation of the glomerular capillary basement membrane.