Rationale and objectives: To evaluate the impact of metabolic parameters in the peritoneal cavity on the likelihood of achieving complete tumor debulking in patients with ovarian and peritoneal cancers. Materials and methods: Forty-nine patients with ovarian and peritoneal cancers were included, who underwent pre-operative 18 F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18 F-FDG PET/CT). The immediate surgical outcome was dichotomized into complete and incomplete tumor debulking. 18 F-FDG PET/CT was qualitatively and quantitatively assessed by scrutinizing 15 anatomical sites for the presence of peritoneal carcinomatosis (PC). Patient-based and site-based diagnostic characteristics were described. Metabolic parameters (SUVmax, metabolic tumor volume and total lesion glycolysis) and the number of 18 F-FDG avid peritoneal sites were evaluated between the two groups. Receiver operating curve (ROC) analysis was performed to determine the optimal cutoff value in predicting incomplete tumor debulking. Results: Twenty-seven out of the 49 patients had PC and 11 had incomplete debulking. Patient-based and site-based accuracies for detection of PC were 87.8 and 97.6%, respectively. The number of 18 F-FDG avid peritoneal sites was significantly different between complete and incomplete debulking groups (0.6 ± 0.8 versus 2.3 ± 1.7 sites respectively, p = 0.001), and the only independent significant risk factor among other metabolic parameters tested (odd ratio = 2.983, 95% CI 1.104-8.062) for incomplete tumor debulking with an optimal cutoff value of ≥4 (AUC = 0.816). Conclusion: The number of 18 F-FDG avid peritoneal sites increased the risk of incomplete tumor debulking after surgery and potentially useful in assisting treatment stratification in patients with ovarian and peritoneal cancers.