In order to develop a model system of infantile hemangioma, transgenic mice were developed carrying the Polyomavirus Middle T (PyMT) gene driven by the SV40 late promoter. From the 520 fertilized eggs surviving microinjection, there were 25 live births. Three of these showed the hemangioma phenotype and carried and expressed the PyMT gene; the remaining descendants were normal. The tumors showed abnormal vascular proliferation with cavernous hemangioma-like structures in the skin surface, tongue, ear mucosa and gastric mucosal tissue in the transgenic mice with hemangioma phenotype. Immunohistochemical staining for Ki-67 was negative, showing the tumors were hemangiomas rather than angiosarcomas. None of the PyMT transgenic mice survived beyond 4 weeks. Previously reported PyMT transgenic mice under the control of various promoters induce many tumor types including hemangiomas. PyMT driven by the SV40 late promoter is an improved model system because it only induces hemangiomas. However, it is limited by the post-natal lethality. Thus, conditional variants of this model system would be desirable.