ObjectiveTo explore the risk factors for lateral lymph node metastasis (LLNM) in medullary thyroid carcinoma (MTC). MethodsA retrospective analysis was conducted on 132 MTC patients who underwent initial treatment in Zhejiang Cancer Hospital from March 2015 to July 2023. Chi-square test, Mann-Whitney nonparametric test and logistic regression were used to analyze the risk factors associated with LLNM in MTC patients by SPSS 22.0 software. ResultsOut of 132 MTC patients, 46 developed LLNM. Multivariate analysis showed that male (female vs. male: OR=0.139, P=0.005), high preoperative calcitonin (Ctn) level (OR=1.001, P=0.042), capsule invasion (OR=15.164, P<0.001), and central lymph node metastasis (OR=4.573, P=0.016) were independent risk factors for LLNM in MTC patients (P<0.05). When the preoperative serum Ctn of MTC patients was greater than 482.50 pg/mL, it indicated a high possibility of LLNM [AUC=0.856, 95%CI (0.791, 0.921)]. ConclusionsGender (male), capsule invasion, high Ctn level, and central lymph node metastasis are independent predictors of LLNM in MTC. For MTC patients with the aforementioned high-risk factors, clinical physicians need to be vigilant about the possibility of LLNM.