A very unusual case of an apparent primary clear cell adenocarcinoma of the vulva in a 57-year-old female is presented. The carcinoma arose in an area of endometriosis within the canal of Nuck in the superior aspect of the right labium majus. Smooth muscle fibers presumably representing remnants of the extrapelvic round ligament were found associated with the endometriosis. Of interest is the fact that the patient underwent right herniorrhaphy 9 years earlier. Although several cases of primary adenocarcinoma arising within the vulva have been reported, none has arisen in areas of endometriosis within the canal of Nuck. No case in the literature of a primary clear cell adenocarcinoma arising from endometriosis in the canal of Nuck and in association with the extrapelvic portion of the round ligament could be found.