The objective of this study was to determine if total laparoscopic hysterectomy using a uterine manipulator with an intrauterine balloon increases the risk of positive peritoneal washings in patients with endometrial cancer. Three sets of peritoneal washings were obtained during surgery from 46 women with endometrial cancer at the Center for Uterine Cancer, National Cancer Center, Korea, between May 2004 and July 2006: the first before the insertion of the uterine manipulator (premanipulator), the second after clipping the fallopian tubes and inserting the uterine manipulator (postmanipulator), and the third after the removal of the uterus through the vagina (posthysterectomy). The cytology samples were examined by the same cytopathologist for the presence of malignant cells. Two of 46 (4.3%) patients were upstaged to IIIA disease due to positive cytology conversion after the insertion of the uterine manipulator, one after the insertion of the uterine manipulator, and the other after the hysterectomy. However, during the follow-up for 3-28 months (median 18), neither of the 2 patients experienced a tumor recurrence. In conclusion, using a uterine manipulator with an intrauterine balloon during the laparoscopic surgery for endometrial cancer might be associated with positive cytologic conversion. Possible explanations are retrograde seeding of tumor cells into the peritoneal cavity, the pressure effect of the inflatable manipulator tip, and spillage of preexited tumor cells between the isthmus and the fimbriae. More effective preventive methods such as distal tubal clipping or coagulation of the fimbriae may be necessary in treating women with endometrial cancer.