It has been known that thyroid stimulating hormone (TSH) stimulates the growth or development of thyroid malignancy and higher serum TSH has association with both thyroid cancer incidence and advanced tumor stage. However, the role of TSH in high-risk features of well-differentiated thyroid cancer was not fully evaluated especially in Asian population. The purpose of our study is to evaluate the association of preoperative serum TSH levels with the advance of differentiated thyroid cancer and its high-risk clinicopathological features in Korean patients. We evaluated 554 patients retrospectively who underwent thyroidectomy and diagnosed as differentiated thyroid cancer during a 3-year period at Pusan National University Hospital. The preoperative TSH levels were significantly higher in the patients with extrathyroidal extension (P = 0.002) and those with lateral lymph node metastasis (P = 0.007). As the increase of the serum TSH concentration, there were significant rising trends in the prevalence of extrathyroidal extension (P = 0.009). In the patients with TSH ≥ 2.5 mIU/L, the prevalences of extrathyroidal extension (P = 0.006) and lateral lymph node metastasis (P = 0.024) were also significantly higher. Using multiple logistic regression, preoperative TSH level was a predictive factor for the presence of extrathyroidal extension (P = 0.008) and lateral lymph node metastasis (P = 0.025). Hashimoto's thyroiditis itself was not associated with the status of extrathyroidal extension and lateral lymph node metastasis. In conclusion, preoperative TSH levels were associated with lateral lymph node matastasis, a novel finding, and extrathyroidal extension in well differentiated thyroid cancer and might be useful as a preoperative supplementary marker for determining the optimal extent of differentiated thyroid cancer surgery in Korean patients.