We compared the adequacy and accuracy of fineneedle aspiration (FNA) with core needle aspiration in a total of 377 patients who underwent both tests. The adequacy rate for core needle biopsy (82.2%) was significantly higher than that of FNA (70.3%; P < .001), but the combined adequacy was significantly higher than that for either test alone (88.9%; P < .001). Overall concordance between the tests was 67.9%. In 70 cases, the core was adequate and negative (55 cases) or atypical (15 cases) and the aspirate was nondiagnostic; in 25 cases, the aspirate was adequate and negative (15 cases) or atypical (10 cases) and the core was nondiagnostic. In 21 cases, the FNA diagnosis was atypical and the core was negative; histologic follow-up supported the FNA diagnosis in all 14 cases with resection, of which 9 were malignant, and 8 of the 9 were papillary carcinoma. On review, it seemed that the core biopsy missed the lesion. Core needle biopsy has a higher adequacy rate than FNA but seems less sensitive, especially for papillary carcinoma. The combination of FNA with core needle biopsy seems to have the highest adequacy rate and sensitivity.