Background: The aim of this study is to identify the inflammatory markers which predict a tubo-ovarian abscess (TOA) in the most accurate way. Methods: This study involves 312 women. Preoperative inflammatory markers in the study group were compared with those in the healthy control group to identify the most efficient predictor of TOA with a high sensitivity and specificity. The recommended cutoff values of the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), white blood cell count, and red cell distribution width were determined using receiver operating characteristic curve (ROC) analyses. Results: The area under the curve (AUC = 0.99) in the ROC analysis was found to be statistically significant for NLR (p < 0.001) with a cutoff value of ≥4.15 (95% CI 0.97-1.00, sensitivity 95.2%, specificity 99.4%). The positive predictive value of NLR was 99.2%, and the negative predictive value was 96.7% (p < 0.001). The recommended threshold for PLR was found to be 164.37 (AUC = 0.95, 95% CI 0.93-0.98, sensitivity 86.7%, specificity 92%), and the cutoff point of the white blood cell count in the ROC analysis was 9.55 × 103/μl (AUC = 0.90, 95% CI 0.87-0.95, sensitivity 78.68%, specificity 96.68%). Conclusion: Preoperative NLR and PLR improve the predictive value of serum markers for the presence of TOA.