Malignant transformation of liver cell adenoma and unequivocal hepatocellular carcinoma in resected liver cell adenomas are rare. We report two cases of liver cell adenoma with concomitant hepatocellular carcinoma. The first occurred in a 19-year-old male with an asymptomatic liver mass and was discovered incidentally. He had a history of nephrotic syndrome treated with oral prednisolone for 15 years. The second occurred in a 46-year-old female who was admitted due to right tubo-ovarian abscess. Computerized tomography scanning incidentally found a 10-cm liver mass in the right lobe. There was no history of oral contraceptive use. Both patients were negative for serum hepatitis B surface antigen and anti-hepatitis C virus antibody. Neither had cirrhosis. These two cases imply that malignant transformation of liver cell adenoma does occur, and that liver cell adenomas should be excised when malignant transformation is suspected.