This is a case report of a testicular papillary serous carcinoma of ovarian type (PSCOT) diagnosed in a 50-year-old man. The tumor presented in the form of multiple papillary exophytic excrescencies on the visceral tunica vaginalis testis lining the inner surface of a hydrocele sac. The tumor was histologically a papillary serous carcinoma with numerous psammoma bodies, indistinguishable from similar tumors arising on the surface of the ovary. Following the tumor's surgical removal, the patient was treated with the same drugs used to treat ovarian serous carcinomas, and he is alive two years after the initial diagnosis. PSCOT must be distinguished from mesothelioma of the tunica vaginalis testis, a tumor with a most unfavorable prognosis. As shown here, immunohistochemical findings can be useful for formulating the correct diagnosis of PSCOT.