The scintigraphic findings in Hashimoto's thyroiditis are highly variable and can mimic any thyroid abnormality. In this study, we compared the scintigraphic findings with ultrasonography in 48 patients with Hashimoto's thyroiditis. Thyroid scintigrams revealed diffuse hyperplasia in 12 patients, multinodular goiter in 20 patients and a solitary nodule in 16 patients (toxic adenoma, n = 1; hypoactive nodule, n = 4; hyperactive nodule with no suppression, n = 3; normoactive nodule, n = 8). Ultrasonography revealed diffuse hyperplasia in 19 patients, multinodular goiter in 20 patients and a solitary nodule in 9 patients. The thyroid scan and ultrasonography revealed the same findings of diffuse hyperplasia in 12 patients and multinodular goiter in 20 patients. Of the 16 patients with a solitary nodule on scintigraphy, only 9 showed the same finding on ultrasonography, with the other 7 showing diffuse hyperplasia. The difference in nodularity between thyroid scanning (74.9%) and sonography (60.4%) has been attributed to pseudonodularity in Hashimoto's thyroiditis. In conclusion, our results confirmed that Hashimoto's thyroiditis can mimic any thyroid abnormality, including diffuse hyperplasia, nodular goiter and multinodular goiter on scintigraphy. Therefore, scintigraphy, ultrasonography and serum thyroid hormone estimation alone may not be helpful for the final diagnosis of Hashimoto's disease. To eliminate unnecessary surgical intervention, all patients should be evaluated by means of physical examination and thyroid autoantibodies, in addition to a thyroid scan, ultrasonography, serum thyroid hormones and fine-needle aspiration biopsy when necessary.