Cystic trophoblastic tumor (CTT) has been described in postchemotherapy retroperitoneal lymph node dissections of patients with testicular germ cell tumors. Prognostically, this lesion is similar to teratoma and no further treatment is required after surgery in the absence of other components. CTT has not, however, been reported in the testis. We identified 14 CTTs in the treated (4) and untreated (9; no information for 1 patient) testes of patients 15 to 43 years old (median, 25) with mixed germ cell tumors. The CTT was a minor component (<1% to 10%) and associated with teratoma (14), embryonal carcinoma (7), yolk sac tumor (7), seminoma (1), and choriocarcinoma (1). At follow-up, CTT and teratoma were also found in 2 subsequent resections (spermatic cord and pelvis mass) in 2 patients. The CTTs were not grossly distinct but on microscopic examination were cystic to partly solid, with cysts often containing fibrinoid material and lined by mononucleated squamoid cells with eosinophilic to pale, frequently vacuolated cytoplasm and having pleomorphic nuclei with dense, often smudged chromatin. Mitotic activity was inconspicuous. Immunostains for hCG (6/6), inhibin (6/6), and p63 (2/6) were focally positive. The pathogenesis of CTT is not completely understood. As untreated patients without choriocarcinoma may have CTT in the testis, it is suggested that testicular CTT represents a form of regressed choriocarcinoma or a late morphologic phase in the transformation of choriocarcinoma to teratoma.