Objective: The factors that influence the acquisition of adequate samples during liquid-based cytology (LBC) remain unclear. This study aimed to identify factors that affect cytological adequacy in LBC after ultrasonography (US)-guided fine-needle aspiration (US-FNA) of thyroid nodules. Study Design: From January 2017 to May 2017, a single radiologist performed US-FNA to diagnose 112 thyroid nodules in 112 consecutive patients. Based on US findings after US-FNA, the size, location, position, composition, calcification, and vascularity of each nodule, as well as the US-based diagnosis, were investigated by the same radiologist. Blinded to US information, a single cytopathologist investigated cytological adequacy, cytological cellularity, and Bethesda category. Results: Of the 112 thyroid nodules, cytological adequacy was achieved in 91.1% (102/112). Thyroid nodules with sizes ≥20 mm or those that were predominantly cystic showed a higher rate of cytological inadequacy (p < 0.05). Thyroid nodule location, position, calcification status, and vascularity did not influence cytological adequacy, nor did US-based diagnosis (p > 0.05). Nodule composition or calcification significantly influenced cytological cellularity (p < 0.05), whereas nodule size, location, position, vascularity, and US-based diagnosis did not (p > 0.05). Conclusions: Most investigated factors did not influence cytological adequacy or cellularity.