Fine-needle aspiration (FNA) biopsy of a thyroid nodule was performed in 797 patients. Ninety-six patients had resection of the thyroid nodule performed subsequent to a one-time FNA biopsy. The surgical pathology of these 96 cases demonstrated a 5.8% false-negative rate and a 9.9% false-positive rate. As a consequence, we prospectively evaluated the routine practice of repeat FNA of cytologically benign thyroid nodules. Repeat FNA confirmed the original benign cytology in 183 (93%) of 196 patients. Seventeen of these 183 patients with benign FNA on both biopsies had resection of the nodule performed because of the development of suspicious clinical signs or in response to the patient's choice; 1 recurrent cyst was found to be carcinomatous. Of the 13 patients demonstrating a change in cytology on repeat FNA biopsy, 9 had a nodule that was classified as possibly malignant (suspicious); 6 of these patients underwent resection, and 1 patient was found to have a carcinomatous nodule. Four patients had nodules that were classified as probably malignant on repeat FNA biopsy; all of their nodules were resected, and three of them were found to be carcinomatous. This study demonstrates that, although one-time FNA biopsy of thyroid nodules is highly accurate, with a relatively low false-negative rate, repeat fine-needle biopsy improves on this diagnostic accuracy, thereby decreasing the risk of misdiagnosing a thyroid nodule that is malignant.