This study aimed to assess the discrepancy rates between initial and surgico-pathological diagnoses in advanced epithelial ovarian carcinoma (EOC) patients treated with neoadjuvant chemotherapy (NAC) followed by interval debulking surgery (IDS), and to identify factors associated with such discrepancies. The retrospective analysis at Siriraj Hospital included all EOC patients who underwent NAC between January 2009 and August 2021. Data were excluded if patients did not have initial histology/cytology investigations or received NAC without IDS, as their diagnostic discrepancies could not be compared. Out of 229 patients, 11 patients (4.8%) had shown diagnostic discrepancies. High CA125 levels (>200 U/ml) corresponded with a lower discrepancy rate (2.9%), while lower levels (<200 U/ml) increased discrepancies to 25.0% (p<0.001). Furthermore, a CA125/CEA ratio ≤ 25 was associated with a discrepancy rate of 75.0%, which decreased to 4.1% when the ratio was > 25 (p<0.001). Diagnostic precision rate across cytology, histology, and combined analyses was similar (p=0.255). The study concludes that significant diagnostic discrepancies (4.8%) are associated with lower CA125 levels and a CA125/CEA ratio < 25. Therefore, clinical, radiological imaging, and tumor markers should be comprehensively evaluated along with cytological or histological results for accurate initial diagnosis before NAC.