Background and Aims: The incidence of papillary thyroid microcarcinoma (PTMC) has been increasing over the past years, and the presence of lateral lymph node metastasis (LLNM) will affect the survival rates of patients. The purpose of this study was to investigate the risk factors and predictive variables for the occurrence of LLNM in PTMC, so as to provide reference for clinical diagnosis and treatment.  
Methods: The clinical data of PTMC patients treated in Dalian Friendship Hospital from January 2015 to June 2020 were retrospectively analyzed. Except for the occurrence of LLNM, the clinical variables observed included sex, age, and the number, size, and location of tumor, as well as the affected glandular lobes, body mass index, and the presence or absence of thyroid capsule invasion, other concomitant thyroid diseases (Hashimoto's thyroiditis, nodular goiter), and combined central lymph node metastasis (CLNM). 
Results: A total of 342 PTMC patients were enrolled, of whom, LLNM occurred in 33 cases (9.6%), CLNM occurred in 142 cases (41.5%), and 25 cases (7.3%) had both CLNM and LLNM. Of the 33 patients with LLNM, 8 cases (24.2%) had no CLNM. Univariate analysis showed that patients with male sex, tumor diameter ≥5 mm, capsule invasion and CLNM were more likely to develop LLNM (all P<0.05). Multivariate analysis showed that the number of CLNM was an independent risk factor for LLNM (OR=1.195, P<0.05). ROC analysis showed that the AUC of CLNM number for estimating LLNM was 0.621, and the cut-off value was 4.5, with a specificity of 0.897 and sensitivity of 0.103.
Conclusion: The number of CLNM is closely related to the LLNM in PTMC patients, which can provide certain quantitative reference for therapeutic lateral lymph node dissection.