Background: An accurate diagnosis of thyroid nodules is crucial for avoiding unnecessary surgical procedures and making timely treatment possible. The objective of the present study was to evaluate the diagnostic accuracy of FNAB (fine-needle aspiration biopsy) using histopathological findings as the reference standards. Patients with the diagnostic categories (DCs) III, IV, V were subjected to a special analysis. In addition, the authors assessed whether other factors, i.e. age, gender, BMI (body mass index), obesity and histopathologically confirmed lymphocytic thyroiditis had an impact on the occurrence of malignant tumors. Methods: A retrospective analysis was conducted on 535 patients who underwent thyroid surgery between October 2022 and September 2023. To assess the FNAB reliability, the result obtained using the Bethesda classification was compared with the histopathological result. Results: The ROM (risk of malignancy) values for DCs I-VI were 38.1%, 15.6%, 29.8%, 18.6%, 91.0%, 93.2%, respectively. DC V (OR 62.34, p< 0.0001) and age≤50 (OR=2.31, p<0.006) had a statistically significant effect on the risk of thyroid cancer. DCs III and IV were not statistically significantly associated with the risk of malignancy (OR=1.68,p=0.16; OR=1.51,p=0.3,respectively). There were no statistically significant differences in sex, BMI and obesity between the patients with benign and malignant lesions. Conclusion: DC V is associated with a high likelihood of malignancy, especially in patients under 50 years of age, and therefore surgery is indicated in this category of subjects. In the DCs III and IV categories, the risk of malignancy is lower and conservative management with active clinical and ultrasound surveillance can be considered. In patients < 50 years of age, with the Bethesda categories III and IV, surgical treatment should be considered.