Objectives: Ultrasonography and fine-needle aspiration biopsy (FNAB) are the gold standard methods in the prediction of benign and malignant thyroid nodules. However, despite being easily applicable, FNAB is an invasive procedure. Less invasive biomarkers should be utilized in the diagnosis of thyroid malignancies. In this study, we aimed to determine the parameters that can be used in the diagnosis of differentiated thyroid cancer (DTC) based on the serum thyroid and thyroglobulin (TG) levels which are routinely checked in patients followed up for thyroid nodules. Methods: In the study, we evaluated patients who underwent thyroid surgery for nodular diseases between January 2015 and June 2022. Of the 1444 patients evaluated, 919 patients who met the inclusion criteria (normothyroid benign nodular disease or normothyroid DTC) were included in the study. Patients were divided into two groups as benign group (BG) and DTC group (DTCG). We compared patients’ pre-operative serum thyroid and TG values and the diagnostic properties of their ratios. Results: Of the 919 patients included, 517 (56.3%) were in BG and 402 (43.7%) were in DTCG. In DTCG, 318 patients were female and 84 patients were male. The mean age in the DTCG was 47.8 years. Comparison of DTCG and BG revealed a significant difference between T3/T4 ratio (p=0.002), T3/TSH ratio (p≤0.001), T4/TSH ratio (p≤0.001), TG/TSH ratio (p≤0.001), and TSH/TG ratio (p≤0.001). However, evaluation of the specified values by ROC analysis showed that the T3/T4 ratio did not make a significant difference be- tween the two groups (p=0.1), whereas the other values displayed a significant difference (p≤0.001 for T3/TSH, p=0.001 for T4/TSH, p≤0.001 for TG/TSH, and p<0.001 for TSH/TG). Conclusion: T3/TSH (cutoff =2.183), T4/TSH (cutoff=0.6), and TG/TSH (cutoff=29.67) values were found to be significant tumor markers for the prediction of malignancy in thyroid nodules, and low values were found to be associated with malignancy. TSH/TG (cutoff=0.031) value was also significant in predicting malignancy while high values were found to be associated with malignancy. Thyroid hormone and TG ratios may alter the preferred treatment method for thyroid nodules.