Abstract Placental site trophoblastic tumor (PSTT) is the rarest type of gestational trophoblastic tumors. Common presentation is irregular vaginal bleeding. A 26-year-old G1P1 woman presented with 15 month amenorrhea, a large uterine mass and plateau low level of serum human chorionic gonadotropin (hCG) which raised the possibility of PSTT. Since whole myometrium had been substituted with the large tumoral mass, hysterectomy was considered despite the young age of the patient. The patient has been in remission 36 months postoperatively without receiving any adjuvant treatment. It seems that plateau low levels of hCG in the presence of amenorrhea should prompt the possibility of PSTT.