Leiomyosarcoma of the inferior vena cava (IVC) is a rare malignant tumor, and only a few cases of the resection of IVC leiomyosarcomas with synchronous liver metastases have been reported. This report describes a female patient who initially presented with a solitary, huge liver tumor and a retroperitoneal tumor. Following our preoperative diagnosis of primary liver cancer with a retroperitoneal lymph node metastasis, the patient underwent combined resection of both tumors. The surgical findings revealed that the retroperitoneal tumor originated from the IVC wall. The pathological and immunohistochemical findings revealed that both tumors were leiomyosarcomas. Although the liver tumor was much larger than the IVC tumor, we considered that the metastatic liver tumor arose from the IVC leiomyosarcoma. This was an instructive case because the metastatic liver tumor from the IVC leiomyosarcoma was so large as to be mistaken for a primary liver tumor.