Herein is reported a case of late-onset pulmonary embolism following pelvic surgery, despite prophylactic measures in the perioperative period. Twenty-six days after hysterectomy and pelvic lymphadenectomy for endometrial carcinoma, an 83-year-old woman developed a pulmonary embolism. This was caused by pelvic lymphocyst, which, in turn, led to chronic compression of the right external iliac vein. This case strongly suggests that prolonged postoperative thromboembolic prophylaxis should be considered in elderly patients undergoing lymphocyst following pelvic surgery.