Purpose: The aim of this study was to evaluate the predictive factors influencing lymph node (LN) metastasis in serosa-penetrating (T3) gastric cancer, and to discern the prognostic factors. Methods: Various clinicopathological factors including age, sex, LN status, tumor growth potential (Ki-67), local immune function (S100), tumor site, macroscopic appearance, tumor size, histologic type, lymphatic and venous infiltration, perineural invasion, pattern of tumor growth margin, stromal reaction were investigated in 105 T3 gastric cancer patients who underwent curative gastrectomy. Results: Among various clinicopathological factors, LN status, tumor size, perineural invasion, pattern of tumor margin and stromal reaction were statistically significant according to univariate survival analysis. In Cox regression analysis, LN status was the most significant prognostic factor (odds ratio; 12.5612). When various clinicopathological factors were compared between the LN positive group (n=66) and the ne- gative group (n=39), lymphocyte infiltration (p=0.008), pushing border (p=0.008), no lymphatic invasion (p=0.002) were more frequent in the LN negative group. On multiple logistic regression analysis, lymphocyte infiltration (odds ratio; 0.2596) and lymphatic invasion (odds ratio; 2.8907) were significant influencing factors for LN metastasis. In the LN negative group, survival in patients with extensive fibrosis was significantly (p=0.0064) poorer than those with no fibrosis. Conclusion: In serosa-penetrating gastric cancer, LN status was the most significant prognostic factor. Lymphocyte infiltration and lymphatic vessel invasion were useful factors in estimating LN metastasis. In the LN negative group with extensive fibrosis, adjuvant treatment will be needed even after curative surgery. (J Korean Surg Soc 2001;60:302-308)