Combined hepatocellular carcinoma and cholangiocarcinoma is a rare tumor. In addition, both hepatocellular carcinoma and cholangiocarcinoma are rarely associated with cystic lesions. We herein present a 62-year-old Japanese woman with combined hepatocellular carcinoma and cholangiocarcinoma which was associated with a rapidly enlarging cystic lesion. Both abdominal ultrasonography and computed tomography revealed a cyst with a solid portion in the left hepatic lobe. A partial hepatectomy was performed on the basis of a tentative diagnosis of a cystadenocarcinoma of the liver, while the diagnosis based on immunohistochemical studies was combined hepatocellular carcinoma and cholangiocarcinoma with cystic formation. The patient died of tumor recurrence, such as intrahepatic metastases and extensive lymph node metastases, 6 months after the operation. The prognosis of this entity, which has never been reported in the English medical literature and is difficult to preoperatively differentiate from hepatic cystadenocarcinoma, therefore seems to be extremely poor.