A case of mature cystic teratoma that contained florid vascular proliferation is reported. The ovarian tumor occurred in a 9-year-old girl; symptoms consisted of vomiting, abdominal pain and a palpable mass. The microscopic findings were mostly typical of a mature cystic teratoma, but also abundant vascular proliferation mimicking hemangioma in association with mature neural tissue was observed. There was a disorganized arrangement of medium- and large-sized spaces lined by cuboidal endothelial cells. Immunohistochemical staining for vascular proliferation showed immunoreactivity for CD31 and smooth muscle actin. Florid vascular proliferation may be seen in association with neural tissue of ovarian teratomas and should not be misdiagnosed as immature teratoma or a vascular neoplasm.
