An 8-year-old previously healthy girl was first seen with vague complaints of abdominal pain. After several months of treatment for constipation, her parents noted abdominal asymmetry and brought her in for reevaluation. Physical examination revealed a large, firm, right-sided abdominal mass that was mildly tender. Computed tomography of the abdomen and pelvis demonstrated a large soft-tissue mass in the posterior right hemiliver (Figure 1), without any evidence of distant disease or disease in the left hemiliver. Results of chest computed tomography and bone scanning also showed no evidence of distant disease. Laboratory data included a normalα-fetoprotein level, and all hepatitis serologic findings were negative.