Four cases of primary malignant melanoma of the vagina in women aged 23, 44, 51 and 65 years are presented. In these 4 cases, thorough clinical and postmortem examinations ruled out the possibility of a primary melanoma elsewhere. The primary tumors showed exophytic growth with superficial ulceration. Three of the melanomas arose from the middle third of the vagina and one from the upper third. Melanin was visible in sections stained with hematoxylin and eosin in 3 of the tumors. In the other one, the first biopsy failed to reveal melanin. However, the second biopsy performed following irradiation showed abundant melanin pigment. Electron microscopic examination of 3 tumors revealed premelanosomes and melanosomes in the tumor cells, thus confirming the diagnosis. Two neoplasms showed atypical histologic features, and only the presence of melanin enabled us to make diagnosis of malignant melanoma. One melanoma was associated with an adjacent widespread intraepithelial component of superficial spreading type indicating its probable mode of origin. All 4 patients died of widespread metastases within 13 months after initial treatment. These 4 cases, in which clinical diagnosis was confirmed by thorough autopsy, strongly indicate that malignant melanoma can arise directly from the vagina.