Objective: To investigate the risk factors of lateral neck lymph node metastasis in patients with papillary thyroid microcarcinoma (PTMC).    
Methods: The preoperative color Doppler results and clinicopathologic data of 462 patients with clinical lymph node negative (cN0) PTMC were retrospectively analyzed. The risk factors for lateral neck lymph node metastasis were determined by χ2 test and Logistic regression analysis.  
Results: In the entire group of patients, the rate of central neck lymph node metastasis was 38.5% and the rate of lateral neck lymph node metastasis was 23.6%. The results of univariate analysis showed that sex (χ2=7.312, P<0.05), tumor diameter (χ2=14.321, P<0.001), thyroid capsule invasion (χ2=21.689, P<0.001), multiple tumors (χ2=13.086, P<0.001), tumor location (χ2=19.028, P<0.001) and central neck lymph node metastasis (χ2=69.421, P<0.001) were significantly associated with lateral lymph node metastasis. The results of multivariate Logistic regression analysis indicated that male sex (OR=1.758), tumor diameter ≥7 mm (OR=1.710), thyroid capsule invasion (OR=3.337), multiple tumors (OR=1.778), central neck lymph node metastasis (OR=7.504) and tumor in the superior pole (OR=4.084) were independent risk factors for lateral neck lymph node metastasis (all P<0.05). The risk of lateral neck lymph node metastasis was increased with the increase of the number of affected central neck lymph nodes (≥3: OR=19.957).
Conclusion: In patients with cN0 PTMC, lateral lymph node metastasis is related to a number of factors. For those who have one or more of them, lateral neck lymph node exploration of the affected side is recommended in the first surgery.