Placental site trophoblastic tumor (PSTT) is the least common form of gestational trophoblastic disease (GTD), and is biologically different from other forms of GTD. There is a wide clinical spectrum of presentation and behavior ranging from a benign condition to an aggressive disease with a fatal outcome. The authors document a case of PSTT on an endometrial polyp. A 51-year-old woman had abnormal vaginal bleeding for the duration of two months. Her past history included a vaginal delivery in 1998. Her physical examination was normal. Tumor markers were at normal levels. Serum β- human chorionic gonadotropin (hCG) level was 19 mIU/ml and human placental lactogen (hPL) level was in the normal range. The patient underwent an operative hysteroscopy. On examination the uterine cavity appeared to be occupied by a pedunculated polypoid neoformation measuring about 2.5 cm in diameter which was removed and later determined to be a PSTT. There were occasional mitotic figures (0-1/10 high power field). The patient underwent hysterectomy and bilateral salpingo-oophorectomy. The patient has no evidence of disease six months after surgery. The authors conclude that a high mitotic count and atypical undifferentiated pathological features are significant poor prognostic factors for survival in PSTT. Hysterectomy represents the gold standard of treatment in all cases of disease confined to the uterus.