An 8-month-old male infant presented with petechiae and severe thrombocytopenia, which was refractory to massive platelet transfusion, intravenous immunoglobulin, and corticosteroid therapy. Disseminated intravascular coagulopathy with enlarged abdominal girth was then identified accidentally. Computerized tomography revealed a huge retroperitoneal mass with an intraspinal extension and spinal-cord compression. Kaposiform hemangioendothelioma with Kasabach-Merritt phenomenon was diagnosed after biopsy. The initial treatment with radiation for spinal-cord decompression was then replaced with interferon therapy. The coagulopathy was corrected promptly, and the tumor shrank gradually. Kaposiform hemangioendothelioma should be considered in the differential diagnosis of retroperitoneal mass lesions during infancy and childhood, especially when refractory thrombocytopenia and coagulopathy exist.