The purpose of this research was to establish whether or not the OVA-LEAK score is superior to clinical criteria (surgeon’s choice) for selecting anastomosis to be protected with a diverting ileostomy, based on previously described and reported anastomotic leak risk factors. From January 2011 to June 2021, a retrospective, multicenter cohort analysis included individuals with primary advanced or relapsed ovarian cancer who underwent cytoreductive surgery with colorectal resection and anastomosis. Patients included in a prior prediction model were excluded from this one. To test the efficacy of the logistic regression model, researchers calculated leakage probabilities in a second, unrelated cohort using the OVA-LEAK formula. The area under the curve (AUC) and receiver operating characteristic (ROC) analysis was then utilized to evaluate the model’s accuracy. Furthermore, an estimate of the Brier score was also made. Each of the predicted performance metrics also has a 95% CI that was computed. The total patient count for validating the multivariable logistic regression model was 848 out of 1,159 recruited patients. Predicting an anastomotic leak in the new cohort yielded an AUC of 0.63. Anastomotic leak sensitivity would be 0.45, specificity would be 0.80, the positive predictive value would be 0.09, and negative predictive value would be 0.97 if a cutoff of 22.1% were used to indicate a positive result (i.e., the presence of a leak). If this threshold is used to identify patients at risk of the leak for bowel diversion, as many as 22.5% of the tested patients would have a diverting ileostomy, and 47% (18/40) of the anastomotic leaks would be ‘protected’ with the stoma. Only 12.5% (5/40) of leaks would be ‘protected’ by a stoma if only the ‘clinical criteria’ for conducting or not performing a diverting ileostomy were taken into account, with the rate of diverting ileostomy reaching as high as 24.3%. Using a predictive algorithm for anastomotic leak instead of subjective clinical criteria improves patient selection for diverting ileostomy without increasing overall stoma usage.