Cystic dilatation of peribiliary glands of intrahepatic and extrahepatic bile ducts was investigated in autopsied livers with adult polycystic disease (n = 8), in autopsied livers with solitary nonparasitic cysts (n = 18) and in normal autopsied livers (n = 23). In normal livers, cystic dilatation of intrahepatic peribiliary glands was absent or slight, when present. In livers with solitary nonparasitic cysts, cystic dilatation of intrahepatic peribiliary glands was present in varying degrees. In livers with adult polycystic disease, intrahepatic peribiliary glands showed frequent and severe cystic dilatation so marked that it was grossly recognizable. In contrast, peribiliary glands of the extrahepatic bile ducts showed no cystic dilatation in most cases, regardless of the three conditions examined. Liver parenchymal cysts were numerous in livers with adult polycystic disease, few in livers with solitary nonparasitic cysts and nonexistent in normal livers. Von Meyenburg complexes were present in 87.5% of livers with adult polycystic disease, in 16.7% of livers with solitary nonparasitic cysts and in 4.3% of normal livers. These findings suggest that intrahepatic peribiliary glands undergo cystic dilatation in livers with adult polycystic disease-and, to a lesser degree and frequency in livers with solitary nonparasitic cysts, probably because of congenital or genetic factors-and that these cystic changes may comprise a part of numerous cysts of adult polycystic disease.