Objective To investigate the characteristics and risk factors of central lymph node metastasis in clinically node negative (cN0) papillary thyroid carcinoma (PTC) (T1 or T2 stage) coexisting with Hashimoto' s thyroiditis (HT).Methods A total of 398 patients undergoing thyroidectomy with central lymph node dissection were enrolled in the study.Patients were divided into the trial group (PTC with HT)and the control group (PTC without HT).The difference of the clinicopathological characteristics between the 2 groups and risk factors for central lymph node metastasis were analyzed.Results Among the total 398 patients,98 (24.6％)had coexistent HT.Central lymph node metastasis rate was similar in the 2 groups (40.8％ vs 41.3％).The number of dissected central lymph nodes was significantly more in the trial group than in the control group (4.9 vs 2.9,P＜0.01) while the number of metastatic lymph nodes had no statistical significance between the 2 groups (1.0 vs 1.0).Univariate analysis showed that tumor size＞1 cm was significantly associated with central lymph node metastasis in the trial group (P＜0.01).Male,＜45 years,tumor size＞1 cm,and tumor located in the middle/lower third of lobe were all significantly associated with central lymph node metastasis in the control group (P＜0.01).Multivariate analysis showed that tumor size＞1 cm was independent predictor for central lymph node metastasis in the trial group,while female,＜45 years,tumor size＞1 cm,and tumor located in the middle/lower third of lobe were all independent predictors for central lymph node metastasis in the control group.Conclusions The number of central lymph nodes was larger in cN0 PTC coexisting with HT patients than that in PTC patients,but there was no statistical difference in the number of metastatic lymph nodes between cN0 PTC with and without HT.Central lymph node dissection is recommended when tumor size 1 cm in cN0 PTC coexisting with HT patients.