The objective of this study was to determine the effects of intraoperative aortic occlusion on blood loss and operative time when used during en bloc resection of internal reproductive organs, pelvic peritoneum, and rectosigmoid colon [modified posterior exenteration (MPE)] for primary cytoreduction of ovarian cancer. Patients undergoing MPE, without palpable distal aortic plaque or calcification, were randomized to: (a) complete distal aortic occlusion (≤60 min, with heparin and protamine reversal) with a vascular clamp immediately before MPE, (b) bilateral hypogastric artery occlusion, or (c) no regional blood flow occlusion. Outcomes were compared with respect to blood loss, operative time, and the transfusion rate (ANOVA analysis of variance). Fifty-six patients were accrued. Groups were equivalent with respect to age, disease severity, extent of upper abdominal surgery done, and cytoreductive outcomes. Aortic occlusion significantly reduced the total operative time (P = 0.02), estimated blood loss (P = 0.01), transfusion rate (P = 0.02), hospital stay (P = 0.05), and both operative time (P ≤ 0.001) and blood loss (P ≤ 0.001) specifically associated with MPE. There were no immediate or delayed complications due to aortic clamping. Aortic occlusion significantly reduces the blood loss and operative time for patients requiring MPE in the context of primary cytoreductive operations.