Objective:To investigate the clinicopathological characteristics of papillary thyroid microcarcinoma in the isthmus (PTMCI) and the independent risk factors of central lymph node metastasis.Methods:58 consecutive patients with PTMCI admitted from Jan. 2016 to Dec. 2018 (isthmus group) were retrospectively analyzed, including 15 males and 43 females,age (42.93±12.69) years old; According to the specific location of papillary thyroid microcarcinoma (PTMC) in isthmus, PTMCI were subdivided into the right PTMCI and the left PT-MCI 67 patients with a single PTMC located in the unilateral lobe were randomly selected as a control (lobe group) , including 13 cases of male and 54 cases of female, age (47.18±11.34) years old. Index included the patient’s age, gender, tumor diameter, TPOAb, aspect ratio, microcalcification, capsular invasion, lymph node metastasis, surgical methods, operation method, and scope of lymph node dissection. SPSS 21.0 software was used for statistical analysis. The quantitative data of normal distribution was expressed as ± s,and the difference between the two groups was compared by chi-square test.The risk factors of CLNM of the isthmus group were analyzed with univariate chi-square test and multivariate Logistic regression analysis.The difference was statistically significant if P<0.05. Results:Compared with PTMC, PTMCI showed a higher rate of capsule invasion ( P=0.003) ,lymph node metastasis ( P=0.049) ,lymph node metastasis in central region ( P=0.033) ,and surgical methods between the two groups were statistically significant ( P<0.05) ;But PTMCI was significantly lower than PTMC in aspect ratio>1 ( P<0.05) . Univariate analysis showed that capsule invasion ( P=0.001) and microcalcification ( P=0.012) were risk factors for PTMCI lymph node metastasis. Multivariate Logistic regression analysis showed that capsule invasion ( P=0.016) and microcalcification ( P=0.046) were independent risk factors for central lymph node metastasis in PTMCI. Conclusions:Compared with PTMC,PTMCI indicates a higher rate of capsular invasion,lymph node metastasis in prelaryngeal and central lymph node;Compared with PTMC, PTMCI indicates a lower rate of aspect ratio>1; Capsule invasion and microcalcification are independent risk factors for central lymph node metastasis in PTMCI. For patients with the right PTMCI or the left PTMCI and also without capsular invasion and calcification,ipsilateral central lymph node dissection should be considered.