Introduction: Polyps are covered with endometrial epithelium and composed of varying proportions of gland, stroma, and blood vessels. Traditionally, endometrial polyps are accepted as a precursor of cancer. The aim of this study was to evaluate the relationship between malignancies arising on endometrial polyps and precursor lesions of these malignancies. Materials and Methods: Data of patients who underwent total abdominal hysterectomy because of a malignancy diagnosed on endometrial polyps were obtained retrospectively from pathology archives. Results: When all malignancies on endometrial polyp were considered, 37% of cases were Type I, 55% were Type II, and 7% were carcinosarcoma. Endometrial intraepithelial carcinoma (EIC) was detected as tumor-adjacent areas on the polyp in eight of the patients who were diagnosed with serous carcinoma. Conclusion: The authors found a precursor lesion in 20 (74%) of their patients who showed endometrial malignancy developing on endometrial polyps. Even when an overt malignancy is not detected on polyps in the curettage material, precursor lesions should be carefully searched.