The femoral vein is named as external iliac vein as it progresses in the cranial direction. In the current case report, a rare variation of the left external iliac vein that was found incidentally during pelvic lymph node dissection in a 36-year-old woman is presented. We also found the same variation at the right side in a 55-year-old woman during laparoscopic pelvic lymph node dissection. Duplication of left external iliac vein throughout its entire length was detected during the operation of the patient with diagnosis of malignant ovarian serous tumor. The other patient with duplication of the right external iliac vein was diagnosed as stage IA, grade 3 endometrial cancer. These rare variations of external iliac veins are of great importance in gynecologic oncologic surgery and other operations requiring pelvic lymph node dissection. Here, we presented and discussed the importance of this variation with the photographs taken during the operation.