PURPOSE: To compare 21 and 27 gauge (G) needles used for fine-needle aspiration (FNA) of thyroid nodules to obtain better specimens for adequacy and cytological diagnosis. MATERIALS AND METHODS: One hundred patients with thyroid nodules (100 nodules) were included in this study. Each nodule was aspirated with both 27 G and 21 G needles. The obtained aspirates were classified as adequate and inadequate by two separate cytopathologists. The results were analyzed by appropriate statistical methods. RESULTS: There was no statistically significant difference between 21 G and 27 G needles in terms of adequacy, according to each pathologist (P > 0.05). After pathological evaluation with consensus, the adequacy prevalence was the same (84%) for both needle types in all study populations (P > 0.05). According to the ultrasound characteristics of nodules, the prevalence of inadequate samples in patients with hypoechoic or heterogeneous nodules was significantly higher compared with the prevalence of inadequate samples in patients with isoechoic or hyperechoic nodules for both types of needles (P < 0.05). However, according to the size of the needles, there was no significant difference between hypoechoic and heterogeneous nodules or between isoechoic and hyperechoic nodules with regard to the ability to yield adequate samples (P > 0.05). CONCLUSION: The results of our study showed that FNA with 27 G needles can aspirate adequate material for cytopathological diagnosis. The probability of inadequate sample aspiration of hypoechoic and heterogeneous nodules is higher than that for other nodule types. © Turkish Society of Radiology 2012.