Objective: To investigate the relationship between the serum thyroid stimulating hormone (TSH) level and the benign or malignant nature of the thyroid nodule(s). Methods: The clinical data of 421 patients with thyroid nodules admitted over the past three years were retrospectively analyzed. Of the patients, 347 cases were diagnosed as benign nodular goiter and another 74 cases were diagnosed as thyroid carcinoma. The difference in serum TSH concentration between the patients with benign and malignant thyroid nodule(s) was compared, and the relevance of the serum TSH concentration to the malignancy risk of thyroid nodule as well as the pathological types of thyroid cancer to serum TSH level were analyzed. Results: The average serum TSH concentration of the thyroid cancer patients was significantly higher than that of the patients with nodular goiter [(2.57±3.32) mIU/L vs. (1.67±2.90) mIU/L] (P<0.05). The malignancy risk of thyroid nodule rose gradually with increasing serum TSH level, and the malignancy rate approached 50.0% as a TSH value exceeded 5 mIU/L. The serum TSH levels among the thyroid cancer patients of different pathological types showed no significant difference (P>0.05). Conclusion: The malignancy risk of thyroid nodule increases with increasing serum TSH level, thus the preoperative serum TSH determination can be exploited as a supplementary index for differentiating the nature of the thyroid nodule(s).