Fine-needle aspiration biopsy (FNAB) is recommended for the initial evaluation of thyroid nodule. If a benign cytology is obtained, suppression therapy with levothyroxine is the first choice in the management of nodular goiter with a follow-up of nodule size with ultrasonography, but the effects of FNAB have not been taken into consideration in this approach. We aimed at evaluating the effect of FNAB on thyroid volume and other ultrasonographic dimensions by measurement of these parameters before and immediately after the procedure, and in later periods, and to clarify the necessity of regarding the effects of FNAB on thyroid. Forty-six patients (34 females, 12 males; mean age: 36.3+/-10.7 yr) with solitary thyroid nodules were included in the study. The nodules were solid in ultrasonography, thyroid function tests were normal and results of FNAB were found as benign cytology. Thyroid hormone suppression therapy was not initiated. Ultrasonographic measurements were made before FNAB, repeated immediately after FNAB, and 1 month and 6 months later. There were no statistically significant changes in the mean thyroid nodule volume, nodule area and circumference of patients before, immediately after FNAB, 1 month and 6 months later. Size differences and individual variability at each time period were analyzed. These parameters changed by more than 10% in a great majority (69.5-78.2%) of patients, and more than 50% change was observed in 17.3-26.0% of patients. Changes in thyroid dimensions were bi-directional, both increment and decrement being noticed. It was thought that this is the reason why there was no significant change in mean nodule volume, area and circumference. Evaluating the difference in nodule volume according to ultrasonographic parameters obtained before FNAB may be misleading because of the individual change in these parameters with FNAB. It may be useful to evaluate the nodule size and volume closely after FNAB to make a true correspondence of these parameters in the long term.