We report a case of extramammary Paget's disease with underlying adenocarcinoma simulating breast carcinoma of the vulva. An 82-year-old woman was found to have a 5 × 3-cm bulky tumor located in the left labium major, infiltrating to the clitoris, left labium minor, and left lateral tissue of the vulva. Small biopsy of the vulva showed intraepidermal proliferation of Paget cells. The patient underwent wide local excision of the vulvar tumor and dissection of left inguinal lymph nodes. Histopathological examination of the resected specimens revealed that Paget cells were distributed singly or tended to form small nests in the epidermis, and that association of these cells with the underlying carcinoma invading to the subcutis could be seen. The underlying carcinoma was composed of squamoid solid nests with central necrotic debris, mimicking ‘comedocarcinoma’ of the breast. In other areas, the tumor cells were present in tubular formations and solid cords reminiscent of invasive ductal carcinoma of the breast. Immunohistochemically, the Paget cells and the underlying carcinoma cells were positive for carcinoembryonic antigen, epithelial membrane antigen, estrogen receptors, and glandular keratins except for CK 20. We speculate that our case is vulvar Paget's disease presenting as a manifestation of underlying breast carcinoma of the vulva, which might have arisen from either the ectopic breast tissue or anogenital mammary-like glands.