The aim of this study is to investigate the effects of the sonographic characteristics of the nodule, demographic features of patient, and nodule size and needle size used for sampling, on obtaining adequate cytological material (CM) in thyroid fine-needle aspiration biopsy (FNAB). We performed 270 FNAB between September 2010 and June 2012. Size, echogenicity, and localization of all nodules were evaluated by ultrasonography (US) before the biopsy. Nodules were grouped as <1, 1-3, and >3 cm according to their size and as hypoechoic, isoechoic, hyperechoic, or heterogeneous according to their US characteristics. 20-, 22-, and 24-G needles were used for the biopsies. Different sonographic characteristics of the nodules did not affect the needle selection. All specimens were classified as adequate or inadequate CM by a cytopathologist. A total of 270 nodules were biopsied, 184 (68.1 %) specimens were considered as adequate CM and 86 (31.9 %) specimens were considered as inadequate CM. Patient age and the presence of heterogeneous echogenicity were found to have prognostic significance in univariate analysis (p < 0.05). In a multivariate logistic regression model with forward stepwise method, advanced age (p = 0.001, OR = 1.042, 95CI 1.018-1.068) and heterogeneous echogenicity (p = 0.017, OR = 1.955, 95CI 1.129-3.385) remained associated with an increased risk of inadequate CM obtainment after adjustment for other potential confounders (nodule size >3 cm and needle size 20-G usage) and variables found to be statistically significant in univariate analysis. Non-diagnostic FNAB remains a significant problem in the evaluation of thyroid nodules and can be as high as 30 %. Inadequate CM rates for elderly patients and heterogeneous nodules were significantly higher than that for other factors. The nodule size and needle size used for sampling did not affect the adequacy of FNAB.