Adenocarcinoma of the vagina is an uncommon tumor. Many theories have been postulated for its etiology and tissue origin. Its occurrence in young women exposed in utero to diethylstilbestrol has pointed to estrogen influence as a possible etiologic factor. A case of adenocarcinoma of the vagina in a patient with gonadal dysgenesis is presented, and histologic and electron-microscopic observations are discussed. This patient is unique in that development of the vaginal neoplasm occurred in the absence of estrogen influence.