Objective: This study aimed to investigate the frequency and characteristic of patients who was pathologically diagnosed with malignancy or premalignancy in women undergoing hysteroscopic endometrial polypectomy for endometrial polyps. Method:We retrospectively investigated 115 patients who were diagnosed as endometrial polyp by transvaginal ultrasonography or sonohysterography and underwent hysteroscopic surgery at our hospital in two years. All surgical specimens were examined histopathologically. Characteristics of the patients including age, size of the largest polyp, desire to bear children, presence of abnormal uterine bleeding and the result of preoperative endometrial cytology were analyzed.Results: Regarding the age, 49 (42.6%) of the EMP patients were in their 30s, which was most common and 65 patients (56.5%) desired to bear children. The polyp size was evaluated before surgery in105 patients and 65patients (56.5%) were medium size (1 cm or larger but below 2 cm). Abnormal uterine bleeding was observed in 46, accounting for 40.0% of all EMP patients. Seven of 115 patients were diagnosed premalignant (3 patients) or malignant (4 patients) on postoperative histopathological examination and 4 of them (premalignant: 3, malignant: 1) desired to bear children. One of the four patients who was diagnosed with malignancy, was a 35 year old nulligravida wishing to bear children with the chief complaint of abnormal uterine bleeding. Endometrial cytology was negative for malignancy, but the very small specimen was subsequently diagnosed as endometrioid adenocarcinoma on pathological examination. Conclusion:We suggest that when masses are found inside the uterine cavity by transvaginal sonography, it is important to carefully examine under sonohysterography and perform pathological examination and treatment using hysteroscopy. Masses should also be examined even if the endometrial cytology is negative for malignancy or the tumor is small, regardless of whether the woman exhibits abnormal uterine bleeding.