Abstract One hundred and thirty-three euthyroid patients with solitary or dominant hypofunctioning thyroid nodules underwent preoperative ultrasonography and needle aspiration cytology. Histological confirmation was obtained in 88 patients undergoing thyroidectomy. Cytological diagnoses included cancer with type, thyroiditis, adenoma, colloid nodule, cyst. Needle aspiration was uncomplicated and did not result in recognizable implantation of tumor. Overall malignancy rate was 17%, with 12 cancers in 75 solid lesions and three cancers in 13 cycstic lesions. Neoplasm rate was 65%, or 88% if colloid nodules were included. Adequate material for cytology, which was obtained in 94% of patients, showed tissue correlation accuracy of 82%. No false positives were reported. False negative reports occurred in 6.4% of all cases, in 4.9% of solid lesions, and in 16.7% of cystic lesions. Correct correlation was seen in 10 of 15 (66%) of malignant cases, with the highest accuracy for papillary (six of seven) and metastatic cancer (two of two) lesions. Needle aspiration is safe, repeatable, simple, and is indicated particularly for patients with nontoxic nodular goiter, who have been assigned to conservative management for various reasons. Needle aspiration cytology provides the clinician with direct information about the thyroid gland that is unobtainable by any other nonoperative technique. However, owing to the possible limitations of this technique, normal or negative needle aspiration cytology does not replace valid, accepted clinical criteria for selection of patients for thyroidectomy to exclude malignancy. To date, implant cancer has not occurred after needle aspiration and therefore the use of this diagnostic technique in the preliminary investigation of nodular thyroid disease is justified.