Biliary cystadenomas and cystadenocarcinomas are rare cystic neoplasms, usually intrahepatic in location, that are characterized pathologically by a multilocular appearance. We report the CT and sonographic findings in eight cases of biliary cystadenoma and three cases of biliary cystadenocarcinoma and correlate them with the surgical and pathologic findings. CT showed internal septa in eight of the 10 multiloculated lesions, whereas sonography showed septa in all five cases in which it was used. CT in two of the three cystadenocarcinomas showed thick and coarse mural and septal calcifications as well as large solid soft-tissue masses in one. CT showed mural soft-tissue nodules in the single case of a unilocular cystadenocarcinoma. Sonogrpahy and CT usually show the multilocular nature of biliary cystadenomas and cystadenocarcinomas. The presence of mural or septal nodules, discrete soft-tissue masses, and possibly thick and coarse calcifications increase the likelihood of a cystadenocarcinoma.