We describe the case of a 72-year-old asymptomatic man with a cholangiocarcinoma arising from a biliary hamartoma, also referred to as "von Meyenburg's complex". The patient was clinically diagnosed as having a cystadenocarcinoma, but the tumor had already been present as a uniformly low-density area on computed tomography taken four years previously, as revealed by retrospective examination of the computed tomography films that had been taken annually after surgery for pulmonary emphysema. The low-density area had continued to enlarge year after year, and a high-density area was observed to have emerged inside the low-density area on computed tomography. Histopathological examination demonstrated that the high-density area corresponded to the cholangiocarcinoma and the low-density area to a biliary hamartoma. This is the first case in which it was possible to confirm the presence of cholangiocarcinoma inside a biliary hamartoma that had continued to increase in size.