One hundred and thirty-nine thyroid nodules were evaluated by aspiration biopsy cytology (ABC) and were compared with the postoperative histologic diagnosis during the period from May 1, 1986 through Aug. 31, 1992. The correlation betwen the two diagnoses proved to be comparable with a low incidence of false-negative diagnoses, but with a relatively high incidence of false-positive ones. The sensitivity was 93.5%, specificity 89.6%, false-negative rate 6.5%, false-positive rate 10.4%, positive predictability 87.9%, negative predictability 94.5%, and overall diagnostic accuracy 91.4%.