Approximately 10% to 20% of thyroid biopsies by fine-needle aspiration (FNA) are nondiagnostic. The management of thyroid nodules in which FNA is nondiagnostic remains controversial because few studies have addressed this issue. We retrospectively reviewed the medical records of 153 patients with nondiagnostic FNAs of the thyroid performed in 1994. Sixty patients had reaspiration biopsies performed. Thirty-seven specimens (62%) were diagnostic and 23 (38%) remained nondiagnostic. Of the 27 patients who had a thyroid operation, 10 (37%) had a malignancy. Preoperative information about physical examination, ultrasound imaging, or nondiagnostic FNA did not predict outcome. Nondiagnostic FNAs of the thyroid may be associated with a high probability of thyroid malignancy. Nondiagnostic FNAs should not be considered benign. Reaspiration followed by selective surgical treatment is recommended.