Needle aspiration biopsies for cytology were performed on 224 patients with thyroid nodules. Diagnosis was confirmed by surgical exploration in 134 patients. Twenty-four biopsies were reported positive for malignancy; 23 were confirmed at operation and there was 1 false positive. Forty-one biopsies were reported benign. Three of these lesions were found to be malignant, representing false negatives. Sixty-nine biopsies were in the questionable category; 16 (23%) of these were malignant. None of the patients suffered complications from the biopsies. Routine employment of needle aspiration biopsy on our service has resulted in a marked increase in the incidence of carcinoma in thyroid nodules selected for surgery. This has resulted from detection of otherwise unsuspected malignancy, as well as avoidance of surgery in patients with benign lesions. Needle aspiration is not a substitute for surgery. It is a valuable diagnostic procedure, and should be performed in the evaluation of essentially all thyroid nodules. We continue to use radioiodine scanning to evaluate our patients, but have found the routine use of ultrasonography unnecessary when needle aspiration is employed. The ultimate decision regarding surgical exploration is based on a combination of factors including history, physical findings, radioiodine scan and needle aspiration biopsy.