To evaluate the potential contribution of high resolution ultrasonography(US) and 99mTc scintigraphy in the routine diagnosis of thyroid nodules, we performed thyroid function tests, US, thyroid scintigraphy, and fine-needle aspiration cytology (FNAC) in all 54 patients who initially visit our surgical department for thyroid masses from March 1995 to February 1996. The final diagnoses were made by either repeated FNAC (n=39) or thyroid operations (n=15). Final diagnoses were adenomatous goiters (n=41), simple cysts (n=3), follicular adenoma (n=1), papillary carcinomas (n=8), follicular carcinoma(n=1). The diagnostic impacts of US and 99mTc scintigraphy in all 54 patients were assessed and scored according to the following criteria: when the information provided by either test supported or confirmed (and/or gave some other information for management of thyroid nodules) the final diagnosis, it received a scores of 2 or 3 respectively, while a score 1 was given when the test itself was useless for the differential diagnosis. The scores of US were higher than those of scintigraphy in the diagnoses of adenomatous goiters, cysts, adenomas and carcinomas. However, after statistical analysis with Wilcoxon's signed rank test, US was statistically superior to scintigraphy only in diagnosing adenomatous goiters. These results indicate that current findings in US for differential diagnosis of thyroid nodules are not absolutely superior to those in scintigraphy, but have some benefits in detection of occult nodules in malignancy and differential diagnosis of adenomatous goiters.