We present the case of a young woman, 22 years old, with an aggressive form of fibrolamellar hepatocellular carcinoma. She began with the signs and symptoms of a hyperammonemic encephalopathy, an uncommon form of presentation. Fibrolamellar carcinoma is a rare liver tumor, which affects young patients without previous liver disease. Its etiology is unknown, and it has been considered as a tumor with a better prognosis than the classic hepatocellular carcinoma.