Portal tract fibrosis with biliary ductular enlargement or proliferation occurs in a number of genetic diseases that have cystic or tubulointerstitial renal lesions. These include some with renal cystic disease such as autosomal recessive diseases (e.g., infantile polycystic disease, juvenile polycystic disease, and Meckel's syndrome), autosomal dominant diseases (e.g., adult polycystic disease) and, rarely, tuberose sclerosis and dominant glomerulocystic disease. Portal tract fibrosis with biliary enlargement and proliferation occurs also with tubulointerstitial kidney diseases. These probably include at least three disorders in the category nephronophthisis-congenital hepatic fibrosis (one autosomal recessive disease and two either autosomal or X-linked recessive diseases) plus Jeune's syndrome (the tubulointerstitial diseases Fanconi's familial nephronophthisis and anti-tubular membrane antibody disease do not regularly cause hepatic fibrosis). Morphometric data on ratios of bile ductules to connective tissue in hepatic portal tracts show high values for infantile polycystic disease (mean, 0.616) compared to lower values for juvenile polycystic disease (mean, 0.286). That the cystic renal lesions of the first two diseases differ in type and time course is known. Similar data on ratios of glomeruli plus tubules to connective tissue in renal cortices and of tubules to connective tissue in outer medullary zones of kidneys, respectively, are as follows: for Fanconi's nephronophthisis, 0.445 and 0.197; for anti-tubular basement membrane antibody disease, 0.585 and 0.164; and for the three types of nephronophthisis-congenital hepatic fibrosis studied, 0.668 and 0.446, 1.39 and 0.921, and 1.18 and 0.12. These data support clinical impressions that the category nephrophthisis-congenital hepatic fibrosis includes more than one disease entity.