ABSTRACT: To assess the ability of preoperative computed tomography (CT) scan of the abdomen/pelvis and serum CA-125 to predict suboptimal (>1cm residual disease) primary cytoreduction in advanced ovarian, fallopian tube, and peritoneal cancer.This was a prospective, non-randomized, multicenter trial of patients who underwent primary cytoreduction for stage III-IV ovarian, fallopian tube, and peritoneal cancer. A CT scan of the abdomen/pelvis and serum CA-125 were obtained within 35 and 14 days before surgery, respectively. Four clinical and 20 radiologic criteria were assessed.From 7/2001 to 12/2012, 669 patients were enrolled; 350 met eligibility criteria. The optimal debulking rate was 75%. On multivariate analysis, three clinical and six radiologic criteria were significantly associated with suboptimal debulking: age ? 60 years (p=0.01); CA-125 ? 500 U/mL (p<0.001); ASA 3-4 (p<0.001); suprarenal retroperitoneal lymph nodes >1cm (p<0.001); diffuse small bowel adhesions/thickening (p<0.001); and lesions >1cm in the small bowel mesentery (p=0.03), root of the superior mesenteric artery (p=0.003), perisplenic area (p<0.001), and lesser sac (p<0.001). A 'predictive value score' was assigned for each criterion, and the suboptimal debulking rates of patients who had a total score of 0, 1-2, 3-4, 5-6, 7-8, and ? 9 were 5%, 10%, 17%, 34%, 52%, and 74%, respectively. A prognostic model combining these nine factors had a predictive accuracy of 0.758.We identified nine criteria associated with suboptimal cytoreduction, and developed a predictive model in which the suboptimal rate was directly proportional to a predictive value score. These results may be helpful in pretreatment patient assessment.