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Background: The incidence of thyroid cancer has more than doubled in recent decades. Debate continues on whether the increasing incidence is a result of an increased detection of small neoplasms or other factors., Methods: Using the Surveillance, Epidemiology and End Results database, we examined the overall incidence of thyroid cancer with variations based on tumor pathology, size, and stage, as well as the current surgical and adjuvant therapy of thyroid carcinoma., Results: Thyroid cancer incidence increased 2.6-fold from 1973 to 2006. This change can be attributed primarily to an increase in papillary thyroid carcinoma, which increased 3.2-fold (P < .0001). The increase in papillary thyroid carcinoma also was examined based on tumor size. Tumors ≤ 1 cm increased the most at a total of 441% between 1983 and 2006 or by 19.2% per year, the incidence of papillary thyroid carcinoma also increased at 12.3%/year in 1.1-2-cm tumors, 10.3%/year in 2.1-5-cm tumors, and 12.0%/year for > 5-cm tumors (all P < .0001 by Cochran-Armitage trend test). We also demonstrated a positive correlation between papillary thyroid carcinoma tumor size and stage of disease (Spearman, r = 0.285, P < .0001). Operative treatment for thyroid cancer also has shifted with total thyroidectomy replacing partial thyroidectomy as the most common surgical procedure., Conclusion: Contrary to other studies, our data indicate that the increasing incidence of thyroid cancer cannot be accounted for fully by an increased detection of small neoplasms. Other possible explanations for the increase in clinically significant (> 1 cm) well-differentiated thyroid carcinomas should be explored., (Copyright © 2010 Mosby, Inc. All rights reserved.)