Nineteen examples of retiform wolffian adenoma previously designated as female adnexal tumor of Wolffian duct origin were studied. The tumors were located in the broad ligament, mesosalpinx, ovary, and retroperitoneum. Grossly, they were wellcircumscribed, generally solid tumors of firm consistency. Microscopically, they were composed of diffuse growth of spindle cells, poorly formed tubules, and sieve—like structures admixed at various proportions. The immunohistochemical characteristics of the 7 tumors evaluated were identical to those of the Wolffian duct remnants stained for comparison. Ultrastructural features of the 2 tumors evaluated, though similar to those of adenocarcinoma of rete testis, were not distinctive and demonstrated variation within the same lesion and between the two cases. None of the women in this series developed subsequent recurrences despite follow—up of up to 15 years. Only one tumor displayed abundant mitotic activity and atypical features; this was a recent case with only 2 years of follow—up, however. Therefore, even though the majority of these tumors behave in a benign fashion, those with increased mitotic activity and atypia warrant close follow—up. Based on the location and morphologic features, the term retiform Wolffian adenoma is proposed as an appropriate substitute for previous designations.