Primary neoplasms of the liver are rare in adolescents and young adults (AYAs), ages 15–39 years, accounting for only 1 % of all neoplasms. Hepatocellular carcinomas (HCCs) are the most common liver tumor seen in AYAs as well as in older adults. Available SEER data have shown a steady increase in the incidence of liver and intrahepatic bile duct tumors between 1976 and 2011 for all age groups and for both sexes. Despite the improvement in diagnosis and treatment, survival of patients with HCCs continues to be dismal. In contrast to older adults in whom almost all cases of HCCs are cirrhosis related, secondary to viral infection or alcohol consumption, less than a third of the AYA patients diagnosed with HCCs have an identifying cause such as hepatitis or other inflammatory liver diseases, and therefore the treatment strategies differ significantly. Children and adolescents with HCC have been treated according to clinical trials designed for the treatment of childhood hepatoblastoma that includes chemotherapy and surgical resection or liver transplant when feasible. On the other hand, treatment for adults with HCC has been based on the extent of disease and liver function. Treatment strategies can be divided in three groups: (1) patients with localized disease (early stage); (2) patients with advanced disease as determined by the extensive hepatic involvement, vascular invasion, or presence of extrahepatic disease; and (3) patients with significant liver dysfunction. Since these strategies are so different, they are discussed separately in this chapter. Given the rarity of malignant liver tumors in the AYA population, national and international collaboration will be essential to evaluate novel therapeutic approaches, to establish the role of liver transplantation for these patients, and to continue to improve our understanding of the biology of HCCs in this population.