Thyroid nodules that exhibit focal uptake of fluorine-18 ((18)F)-fluorodeoxyglucose (FDG) are relatively frequent. Although the clinical features and associated mechanisms of FDG-avid lesions in both thyroid cancer and cytologically indeterminate nodules have been extensively studied, not much information is available on benign nodules. Therefore, in this retrospective study, the clinical, serological, and sonographic features of 15 benign FDG-avid nodules were compared with those of 17 non-avid lesions. Univariate analysis indicated that the FDG-positive and -negative nodules were similar with regard to age, gender, thyroid stimulating hormone (TSH), anti-thyroglobulin antibodies, tumor size, 4 B-mode sonographic findings (i.e., shape, margin, texture, and echo level), and/or elasticity. The presence of intranodular blood flow and the absence of a cystic component were associated with a greater possibility of positive FDG uptake. Multivariate analysis showed that vascularity was the only independent factor predicting FDG uptake. Across a wide range of tumor types, the extent of FDG uptake is positively correlated with tumor perfusion; this observation is consistent with the results of this study, which shows that FDG uptake in benign thyroid nodules is associated with increased vascularity.