Testicular or paratesticular neoplasms that resemble the common epithelial type of ovarian tumor are quite rare. The authors report the case of a 29-year-old man with a metastatic serous papillary adenocarcinoma arising from the tunica vaginalis. To the authors' knowledge, this is the first reported case of a serous carcinoma of the tunica vaginalis behaving in a malignant fashion. The fact that clinically apparent metastatic disease occurred 4 years after initial presentation suggests that development of metastases is a late event. Unfortunately, the tumor has been refractory to therapy with chemotherapeutic agents with activity against ovarian malignancies.