We herein report a 64-year-old Japanese woman with cystadenocarcinoma of the liver without mesenchymal stroma which had been followed up by imagings for 12 years. A small round cyst grew from 1cm to 4 cm in diameter during 10 years. Thereafter, solid components were first detected in the unilocular cystic mass, which showed very rapid growth. Extended right lobectomy with right caudate lobectomy was performed. The histopathological diagnosis was cystadenocarcinoma of the liver without mesenchymal stroma. In this communication, we describe the progressive morphologic changes, shown on imagings, from a benign hepatic cyst to cystadenocarcinoma of the liver without mesenchymal stroma, and we briefly discuss the carcinogenesis of cystadenocarcinoma of the liver.