BACKGROUND: This study evaluated the effectiveness of preoperative inflammatory response markers in distinguishing clear cell carcinoma (CCC) and endometrioid carcinoma (EC) from ovarian endometrioma. METHODS: Patients with stage I ovarian cancer with histology CCC/EC or endometrioma who underwent surgery at our institution between 2010 and 2021 were included. Preoperative inflammatory response markers evaluated were white blood cell count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), fibrinogen, D-dimer, neutrophil/lymphocyte ratio (NLR), platelet count/lymphocyte ratio (PLR), and systemic immune-inflammation index (SII). The tumor markers CA125 and CA19-9 were analyzed. The median values of these markers were compared between the CCC/EC and the endometrioma groups. The areas under the curve (AUC) in Receiver Operating Characteristic analysis were compared. RESULTS: Fifty patients with stage I CCC/EC and 247 patients with endometrioma were included in the study. Inflammatory response markers were significantly higher in CCC/EC cases than in endometrioma cases ( CONCLUSION: Inflammatory response markers may be useful for the detection of stage I ovarian cancer. Notably, the NLR or SII, calculated using a complete blood count, appears particularly efficient. Combining tumor and inflammatory response markers may enhance diagnostic accuracy in distinguishing ovarian cancer from endometrioma.