Clear-cell carcinomas of the female genital tract are uncommon tumors that usually arise in the ovary, cervix, or vagina. The objectives of the present study were to examine the immunohistochemical and ultrastructural characteristics of 18 of these tumors and to determine whether any distinctive features were present at the different locations. The fine structure of the neoplastic cells was similar at the several sites but there was a striking difference in the appearance of the basal lamina. Prominent reduplication of the basal lamina was seen in all 7 ovarian carcinomas, whereas it was mild in 3 and absent in 7 of the cervico-vaginal tumors. The distribution of eosinophilic hyaline material in hematoxylin/eosin sections and of immunohistochemical staining for type IV collagen and larminin correlated with the ultrastructural observations. Reduplication of the basal lamina has been observed in a number of epithelial neoplasms and viewed as a criterion of differentiation, but there is currently no evidence that its presence influences the prognosis of clear-cell carcinomas of the ovary.