Partial nodular transformation of the liver (PNT) is a rare condition of unknown pathogenesis in which nodules composed of hepatocytes replace portions of the parenchyma. There is usually evidence of portal hypertension and portal vein thrombosis. We present a case of PNT in a man with persistent ductus venosus and hypoplasia of the major intrahepatic portal veins but without evidence of portal hypertension or portal vein thrombosis. Portal venules were largely absent between nodules, as documented by morphometry. We suggest the pathogenesis of PNT is similar to that previously proposed for nodular regenerative hyperplasia, that is, atrophy occurs in parenchyma with insufficient blood supply and nodules arise by hyperplasia in areas with adequate supply. Partial nodular transformation and nodular regenerative hyperplasia differ mainly in the cause and distribution of the portal vein obliteration.