Cystic trophoblastic tumor (CTT) is an uncommon lesion that is usually seen after chemotherapy in patients with testicular germ cell tumors. Its clinical significance has not been well studied. We identified 17 patients with CTT in retroperitoneal lymph node dissections (RPLNDs) after cisplatin-based chemotherapy for testicular germ cell tumors. None had other forms of persistent germ cell tumor except for teratoma, and no patient received additional chemotherapy after RPLND. At the time of RPLND, 7 patients were known to have had normal serum levels of beta-subunit of human chorionic gonadotropin (beta-hCG), whereas 5 had relatively mild elevations (1.6-165 mIU/mL, median, 8.0 mIU/mL). The CTTs consisted of circumscribed, small cysts, usually multifocal, lined by mostly mononucleated trophoblast cells with abundant eosinophilic cytoplasm, often with smudged nuclei and showing only infrequent mitotic figures. Although the epithelial lining was often stratified to several layers in thickness or formed intracystic papillary tufts, solid proliferations of trophoblast cells within the stroma were absent, as were clearly biphasic admixtures of mononucleated and multinucleated trophoblast cells. The cysts were either empty or contained fibrinoid material and were set in a hypocellular, fibrous stroma with adjacent teratoma. Stains for hCG highlighted rare cells. On follow-up of 15 patients, 11 were disease free (mean, 80 months). Three recurred with serum alpha-fetoprotein elevations at 25, 31, and 107 months, respectively, and one with beta-hCG elevation at 2 months. The latter patient, however, also had unresected mediastinal tumor postchemotherapy. We conclude that the finding of CTT in postchemotherapy resections does not warrant additional chemotherapy. Its clinical significance appears similar to that of residual teratoma.