Background. Giant liver hemangioma >20 cm may cause severe complications; therefore, operative treatment can be highly difficult and risky. No studies have been performed to determine the characteristics of this subgroup. Methods. A retrospective study was performed on 141 patients who underwent operative treatment for liver hemangioma. The patients were divided into an extremely giant hemangioma group (>20 cm, 36 cases) and a giant hemangioma group (> 10 cm but <20 cm, 105 cases). A comparison was then made between the groups. For patients in the extremely giant hemangioma group, further comparison was also made between liver resection and enucleation. Results. Compared with the giant hemangioma group, patients in the extremely giant hemangioma group had greater rates of leukopenia (P <.001), anemia (P <.001), thrombocytopenia (P <.001), pancytopenia (P <.001), prolonged prothrombin time (P <.001), and Kasabach-Merritt syndrome (P =.001). Patients in the extremely giant hemangioma group also had greater rates of compression of the hepatic vein (P <.001), inferior vena cava (P <.001), and porta hepatis (P <.001). The extremely giant hemangioma group had more blood loss (P <.001) and autologous transfusion (P <.001), greater rates of blood transfusion (P <.001), and greater postoperative stays (P <.001). Morbidity was greater in the extremely giant hemangioma group; however, this difference was not statistically significant (P =.076). For patients in the extremely giant hemangioma group, no differences were detected regarding autologous transfusion, blood transfusion, or morbidity between enucleation and liver resection. Conclusion. Extremely giant hemangiomas may cause abnormalities in the hematologic and coagulation systems. Operative treatment may be difficult and risky but can be completed safely.