We evaluated the preoperative serum thyrotropin (TSH) levels in 386 patients operated on for nodular thyroid disease (NTD). TSH levels for cases with final benign disease and differentiated thyroid carcinoma (DTC) were compared. No evidence of cancer was detected in 310 patients (80.3%), whereas malignancy was present in 76 cases (19.7%). Mean TSH concentration was 1.36 ± 1.62 mU/L in benign patients and 2.08 ± 2.1 in cases with malignant lesions (P = 0.0013). The group of malignancy was subdivided in papillary thyroid carcinoma (PTMC) versus thyroid cancer of larger size (TCLS). Mean TSH was 1.71 ± 1.52 in PTMC and 2.42 ± 2.5 in TCLS. Significant differences were found when all groups (benign, PTMC and TCLS) were compared (P < 0.001). However, pairwise comparisons between them showed that differences were only significant between benign and TCLS groups (P < 0.01). In conclusion, TSH levels were higher in patients with a final diagnosis of DTC. Moreover, it appears that there exists an increment in tumor size as a function of increment in the TSH level.