Kaposi's sarcoma (KS) is one of the most common diseases seen in patients presenting with acquired immunodeficiency syndrome (AIDS); however, it is rare in Japan. We herein report a case of AIDS-associated KS of the tongue, which was initially misdiagnosed as recurrent hemangioma according to the initial histopathological diagnosis. The patient is a 42-year-old male who had been suffering from a painful vascular neoplasm-like mass on the dorsum of the tongue. The patient did not complain of any other distinct symptoms and a debulking operation was planned based on the clinical diagnosis of hemangioma. However, preoperative blood tests revealed the presence of syphilis and the human immunodeficiency virus and the patient was therefore diagnosed to have full-blown AIDS. Therefore, the patient's oral lesion was then instead suspected to be oral KS (OKS). A histopathological examination of the tongue biopsy specimen showed the typical findings of KS. Combination active antiretroviral therapy (cART) combined with liposomal doxorubicin was administered and the patient achieved a complete remission (CR). In conclusion, clinicians including oral surgeons, should take OKS into account in the diagnosis of vascular neoplasm-like masses of the tongue in adults since this complication may occur as a result of AIDS. © 2012 Asian AOMS, ASOMP, JSOP, JSOMS, JSOM, and JAMI.