Abstract Disclosure: M. Romero Ibarguengoitia: None. I.A. Villarreal-Ondarza: None. J. Mercado Basurto: None. A. González Cantu: None. The diagnostic performance of ultrasonographic ACR-TIRADS classification to evaluate thyroid nodules is poorly studied in a Mexican population. The aim was to assess the diagnostic accuracy of ACR-TIRADS classification for identifying malignant thyroid nodules in adults aged >18 years. This retrospective research study was conducted in 4 medical centers in Northern Mexico from 2022 to 23 to obtain ACR-TIRADS classification of nodules from thyroid ultrasound. Information about Bethesda classification after fine needle aspiration and cytology from thyroidectomy was analyzed for diagnostic performance tests. A total of 160 patients were included. Thyroid nodules were classified as TIRADS 3 in 12%, TIRADS 4 in 44%, and TIRADS 5 in 41%. Twenty-six (16%) were classified as Bethesda 1, 39 (24%) were classified as Bethesda 5, and 30 (19%) were classified as Bethesda 6. The sensitivity (S) of TIRADS 4 was 41%, specificity (E) was 50%, positive predictive value (PPV) was 59%, negative predictive value (NPV) was 32%, and accuracy was 44%. The S of TIRADS 5 was 51%, E 77%, PPV 80%, NPV 47%, and accuracy of 61%. When comparing with other populations, the performance was the same as the Turkish (their accuracy was 59.93%) population but lower than a population from China (their accuracy was 86%) and Germany (PPV 100% for TIRADS 5). The proportion of malignancy in our sample compared with a reference sample from Germany was lower, 36 vs. 85% for TIRADS 3, 59 vs. 85% for TIRADS 4, and 80% vs. 100%, p< 0.001. Concerning Bethesda's classification, the proportion of malignancy was the same according to the reference sample from the American Thyroid Association. In conclusion, there was a moderate accuracy of the ACR-TIRADS classification system in our population, the same in comparison with the Turkish population; slightly lower than what is reported in a population from Germany and China. Presentation: 6/1/2024