It used to be said that solitary thyroid nodules are more likely to be malignant than multinodular goiters. This concept was based on physical examinations. However, with advances in ultrasonography many multiple nodular goiters are being detected. So, it has become more difficult to diagnose multiple nodular goiter accurately as benign or malignant. We studied the findings of ultrasonography, fine needle aspiration biopsy (FNA), and postoperative histopathological examination of 197 nodules in 61 patients with multiple nodular goiters operated on in the past three years. One or more malignant nodules were found in 44 patients (72. 1%). The sensitivity for malignancy of FNA was 67. 6% and the specificity was 91. 7%. Of the FNA positive group 90. 9% proved to be malignant and of the FNA negative group 50. 0% proved to be benign on histopathological examination after surgery. The finding of calcification on ultrasonography was significantly correlated with malignancy (p &lt
0. 01), sensitivity was 84. 1% and specificity was 64. 7%. Of the goiters with calcification 86% proved to be malignant and of those without calcification 61. 1% proved to be benign on histopathological examination. It is concluded that the diagnosis of multinodular goiter is more accurate when both FNA and ultrasonography are used. Multiple nodular goiters of class I or II without calcification are considered to be benign, and multiple nodular goiters of class III, 1V, or V and those of class I, II with calcification are considered to be malignant. With these standards, 86% of the goiters provisionally diagnosed as malignant proved to be malignant, and 90. 9% of those considered to be benign proved to be benign on histopathological examination after operation. Therefore, goiters with class I or II of FNA findings and no calcification on ultrasonography can be observed as benign, if they are small. Other goiters should be operated on, because they may be malignant. © 1994, The Society of Practical Otolaryngology. All rights reserved.