Background/Aim: We investigated the predictive value of scoring systems of peritoneal disseminations for complete surgery (CS) at primary debulking surgery (PDS) in advanced ovarian cancer. Patients and Methods: We retrospectively enrolled eligible patients with clinical stages III or IVA selected for PDS from January 2015 to December 2019. Concern variables were predictive index value (PIV) and peritoneal cancer index (PCI) from operative and pathological reports. Primary endpoints were cutoffs to predict operative completeness using the receiver operating characteristic curve. Results: Among 111 patients, PIV ≥8 and PCI ≥13 were the best predictors of incomplete PDS, including optimal and suboptimal surgeries (AUC=0.821 and 0.855, respectively). CS rates in PIV ≤6 and PCI ≤12 were significantly higher than in PIV ≥8 (89.3% vs. 47.2%; p<0.05) and PCI ≥13 (90.9% vs. 41.2%: p<0.05). Conclusion: PIV and PCI are potential predictors for CS at PDS. Every year, numerous patients suffer from ovarian cancer, the seventh most prevalent malignant tumor in women, with almost 240,000 newly diagnosed cases annually, as well as the eighth most common cause of female cancer death, with almost 150,000 deaths annually worldwide (1). In Japan, the incidence of ovarian cancer has been increasing up to 15.0 per 100,000 women, almost half of whom were newly diagnosed as advanced ovarian cancer (AOC) with International Federation of Gynecology and Obstetrics (FIGO) stage III and IV (36.2% and 10.0%, respectively) (2).Complete resection in primary debulking surgery (PDS) is considered the most favorable therapeutic option for AOC (3). Recently, several randomized control trials (RCTs) compared the postoperative prognosis between PDS and interval debulking surgery (IDS) after neoadjuvant chemotherapy (NAC) (4-7). Of these trials, the EORTC and CHORUS studies showed non-inferiority of IDS to PDS (4, 5). In the SCORPION trial, NAC + IDS was not superior to PDS in improving prognosis, but the authors considered NAC + IDS as an acceptable strategy for patients with large dissemination burdens because the incidence of operative complications was less than that for PDS (7). Although other RCTs are ongoing to clarify therapeutic superiority of PDS to overcome the limitations in previous studies, such as the low rate of complete surgery (8, 9), gynecologists need to pursue complete surgery in PDS (complete PDS), and if it seems difficult, consider NAC + IDS. Therefore, in deciding on operative options for AOC, a reliable predictive model for operative completeness in PDS based on preoperative examinations should be established.Recently, diagnostic laparoscopy has been indicated as the safest method for tumor biopsy in AOC cases, and it has been also established as a potential strategy for detecting cases with large disseminations likely to result in suboptimal surgery in PDS (10). Furthermore, some quantitative scoring systems for abdominal disseminations, such as predictive index value (PIV) and Peritoneal Cancer Index (PCI), have been used ...