Hepatoblastoma is the most frequently occurring liver tumor in children, accounting for over 25% pediatric hepatic tumors and nearly 50% of those that are malignant. Histologically, the tumor can be divided into the following six patterns: (1) fetal epithelial; (2) embryonal and fetal epithelial; (3) macrotrabecular; (4) small cell undifferentiated; and (5) mixed epithelial and mesenchymal type with teratoid features or (6) without teratoid features. Immunohistochemical studies display a wide variety of immunostaining with monoclonal antibodies particularly those specific for epithelial-derived components. Tumor cytogenetics show a high incidence of trisomy 20 and trisomy of all or part of chromosome 2. The developing liver displays many features similar to those seen in hepatoblastoma, including uniform hepatocytes and cords two cells thick separated by sinusoids displaying hematopoiesis. Hepatoblastomas display only minimal ductular differentiation, similar to the fetal development of the liver that does not display significant ductular development until well into the second trimester.