Kidney fragments from two cases of hereditary polycystic kidney disease (adult form) at an early stage were examined by microdissection. Localized cystic cystic dilatations were found in proximal and distal tubules, loops of Henle, and collecting tubules. Entirely normal nephrons and collecting tubules were also observed. Abnormal branching of collecting tubules or the abnormal attachment of nephrons, as described in other microdissection studies, were not found. Our observations do not confirm the hypothesis that the adult form of hereditary polycystic kidney disease is the consequence of ampullary dysfunction during early development.