Kasabach-Merritt syndrome denotes profound thrombocytopenia and coagulopathy in an infant with a vascular tumor. A retroperitoneal vascular tumor with an unusual combination of histopathological features is reported, and compared with vascular lesions described in the reported cases of Kasabach-Merritt syndrome in the literature. A large retroperitoneal tumor that had expanded through the sigmoid mesocolon into the sigmoid colon wall was resected from an 8-month-old infant with fully developed Kasabach-Merritt syndrome. Histological examination revealed a combination of venous (cavernous) malformation, kaposiform hemangioendothelioma and tufted angioma-like areas. Cellular tumor components (especially tufted angioma-like parts) infiltrated the wall of the sigmoid colon to the submucosal level. Immunohistochemical staining with antibodies to the Ki-67 antigen and proliferating cell nuclear antigen showed a low proliferative activity, whereas the antiapoptotic bcl-2 protein was expressed diffusely in tumor cells. This is the first reported case of a vascular tumor with tufted angioma-like elements found in the retroperitoneum, and the first reported in combination with kaposiform hemangioendothelioma and venous malformation in the same lesion. Considering the immunohistochemical results and overlapping histological features, it may be considered that tufted angioma and kaposiform hemangioendothelioma represent different growth patterns or stages in the development of a single type of hemangioma.