<h3>Introduction/Background</h3> The aim of this study was to perform a diagnostic accuracy evaluation of the International OvarianTumor Analysis (IOTA) – Assessment of Different NEoplasias in the adneXa (ADNEX) model for the diagnosis of borderline ovarian tumours (BOT). <h3>Methodology</h3> A retrospective study of patients who underwent gynaecological surgery between 2012 and 2022 with a previous diagnosis of adnexal mass by transvaginal ultrasound at a tertiary referral university hospital with a specific gynaecological oncological unit. Sociodemographic data, ultrasound information, and pathological findings were retrieved from the patient's medical records. The IOTA ADNEX model was used to estimate the probability of benignancy or malignancy (borderline, stage I, stages II-IV, or metastatic) with a threshold of 10%. Definitive pathology was the reference standard used. Sensitivity, specificity, positive (PPV) and negative predictive values (NPV), and likelihood ratios (LR) were calculated. <h3>Results</h3> A total of 757 patients underwent surgery and had a pathology report. The IOTA ADNEX model identified 586 (77.6%) masses as benign and 171 (22.4%) as malignant. Of those identified as malignant, 64 (37.4%) were identified as borderline by the IOTA ADNEX model, and pathology identified 18 (28%) as BOT. These women had a mean age of 39 (±) 17 years, 11 (73%) were premenopausal, their median CA 125 was 115 (±) 32 U/mL The IOTA ADNEX model had a sensitivity, specificity, PPV, NPV, LR(+) and LR(-) of 72%, 68%, 28%, 93%, 2.28 and 0.40, respectively for the diagnosis of BOT <h3>Conclusion</h3> This diagnostic accuracy study showed that the IOTA ADNEX model has good sensitivity in diagnosing BOT in our center. However, its regular performance in the likelihood ratio could suggest the need to incorporate additional variables in the ultrasound findings.