Background and Aims: There is a close relationship between lymph node metastasis and the prognosis of the gastric cancer patients, and the presence or absence, as well as the degree of lymph node metastasis are crucial for treatment decision making of the patients. However, there are still many challenges in preoperative evaluation of the lymph node metastasis. The purpose of this study is to investigate the relevant risk factors for lymph node metastasis in gastric cancer patients, so as to provide certain way criteria for predicting lymph node metastasis before operation. 
Methods: The clinical and follow-up data of 380 patients with gastric cancer treated during January 2014 to April 2015 were reviewed. The relationship between lymph node metastasis and the relevant clinicopathologic factors of the patients were analyzed, in which, the risk factors for lymph node metastasis of gastric cancer were determined. Further, the efficiencies of the risk factors for predicting lymph node metastasis in gastric cancer were assessed by ROC curve, and the impacts of the risk factors on the prognosis of the patients were analyzed by Kaplan-Meier method.
Results: Of the 380 patients, lymph node metastasis occurred in 241 cases (63.42%). The results of univariate analysis showed that BMI, depth of tumor invasion, degree of differentiation, Lauren’s classification, tumor diameter and tumor marker CA125 were significantly associated with the metastasis of lymph node in gastric cancer (all P<0.05); the results of multivariate analysis revealed that BMI (OR=4.175, P=0.041) and the depth of tumor invasion (OR=16.444, P<0.000 1) were independent risks for lymph node metastasis; the results of correlation analysis demonstrated that there was a significant positive correlation between the positive rate of lymph node metastasis and BMI value (r=1.95, P=0.007). BMI (using 24 kg/m2 as a cut-off value) and depth of tumor invasion (using T4 stage as a threshold) had a same sensitivity of 63.16% and a specificity of 76.84% and 53.68% respectively for predicting the presence or absence of lymph node metastasis in gastric cancer; the specificity of their combined use was increased to 88.36%, and the area under the ROC curve reached 75.76%. The results survival analysis showed that the 3-year overall survival rate in patients with high BMI value was significantly lower than that in patients with low BMI value (51.09% vs. 53.13%, P<0.05). 
Conclusion: BMI and depth of tumor invasion are independent risk factors for lymph node metastasis in gastric cancer. Patients with high BMI value may face an increased risk of lymph node metastasis in gastric cancer. The combined consideration of BMI and depth of tumor invasion may have certain practical value in predicting lymph node metastasis before operation.