Abstract Reliance on fine-needle aspiration (FNA) of the thyroid as the key determinant whether to observe only or proceed surgically is predicated on achieving a minimal false-negative error rate (the incidence of malignant disease in nodules diagnosed benign by means of FNA). To provide convincing data that malignant disease has not been overlooked requires extended follow-up on a large' number of patients with cytologically benign lesions. The intent of our study was to assess the long-term accuracy of thyroid FNA-based diagnoses—particularly with respect to false-negative errors. From our total experience of more than 8000 patients, we reviewed the cases of 680 patients who underwent FNA in 1980, the first year we used it clinically. Follow-up information was obtained on 641 (94%) of the patients with a mean time since FNA of 6.1 years. Benign cytologic findings were reported on 439 (68%) of these patients, and only three (0.7%) had false-negative diagnoses. The false-positive rate was 0% for the 24 (4%) patients with positive aspirates. FNA is a safe, reliable, effective means of accurately discriminating benign from malignant thyroid lesions.