Objective To investigate the influence of combined Hashimoto''s thyroiditis（HT） on the diagnostic accuracy of ultrasound-guided fine-needle aspiration cytology（US-FNAC） for thyroid nodules.Methods The medical records of 1159 patients (a total of 1383 nodules) with thyroid nodules who underwent US-FNAC and subsequent surgical resection in our hospital were collected. Based on the presence of HT, the nodules were divided into HT+ group (456 nodules) and HT- group (927 nodules). The diagnostic performance of US-FNAC for both groups was compared using surgical pathology as the gold standard. Results The sensitivity, negative predictive value, and accuracy of US-FNAC for HT+ group nodules (96.0%、40.7%、94.3%) were all lower than those for HT- group nodules (98.8%、73.0%、97.1%), and the false-negative rate (4.0%) was higher than that of the HT- group (1.2%), with all differences being statistically significant (P＜0.05). Further analysis showed that for nodules with a maximum diameter ≤10mm, the sensitivity, positive predictive value, and accuracy of US-FNAC for HT+ group (96.2%、97.5%、94.0%) were all lower than those for HT- group (98.8%、99.3%、98.2%), and the false-negative rate (3.8%) was higher than that of the HT- group (1.2%), with all differences being statistically significant (P＜0.05). For nodules with a maximum diameter ＞10mm, there were no statistically significant differences between the two groups.