Ectopic breast tissue has been described rarely in the vulva and is known to develop a variety of pathologic changes. Our review of the literature found a total of 11 reported cases of primary infiltrating ductal adenocarcinoma arising in ectopic breast tissue of the vulva. We report what we believe is the first case of primary mucinous adenocarcinoma arising in ectopic breast tissue of the vulva diagnosed by characteristic histopathologic features and immunohistochemical stain results. We discuss the criteria used in diagnosis of primary breast carcinoma of the vulva and review previously reported cases.