Background/Aims: To characterize ultrasonographic findings in papillary thyroid carcinoma (PTC) combined with Graves’ disease. Methods: Medical records and ultrasonographic findings of 1,013 patients with Graves’ disease and 3,380 patients without Graves’ disease were analyzed retrospectively. A diagnosis of PTC was based on a pathologic examination. Results: The frequency of hypoechogenicity was lower in patients with PTC and Graves’ disease than in patients with PTC alone (p < 0.05). The frequency of perinodular blood flow in patients with PTC and Graves’ disease was significantly higher than in those with PTC alone (p < 0.05). PTC combined with Graves’ disease was characterized by more ill-defined borders and less frequency of overall calcification, punctate calcification, and heterogeneous echogenicity, although the difference was not statistically significant. Conclusions: Our results suggest that patients with Graves’ disease more frequently have atypical PTC findings on ultrasonography. (Korean J Intern Med 2010;25:71-76)