OBJECTIVE To evaluate the impact of lymph node metastasis on the prognosis of gastric cancer without serosal invasion. METHODS From January 1994 to December 2005, 616 gastric cancer patients without serosal invasion and 162 gastric cancer patients with serosal invasion underwent D2 or D2(+) lymphadenectomy. Clinicopathologic data and long-term survival of the two groups were analyzed retrospectively. RESULTS The 5-year survival rate of patients with gastric cancer without serosal invasion was 77.9%, significantly higher than that of patients with gastric cancer with serosal invasion (37.3%) (P<0.01). The 5-year survival rates of T1a(M), T1b(SM), T2(MP), T3(SS), T4(SE,SI) were 95.6%, 92.5%, 73.5%, 62.7%, and 37.3%, respectively. As classified in the 13th edition of Gastric Cancer Treatment Guidelines in Japan, the 5-year survival rates of patients with gastric cancer without serosal invasion were 91.5% in N0, 75.3% in N1, 54.8% in N2, 14.7% in N3, and the differences were statistically significant (P<0.01). According to 7th edition of TNM classification, the 5-year survival rates of N0, N1, N2, N3a, N3b for the study group were 91.5%, 83.6%, 59.8%, 17.2%, 11.8%, respectively (P<0.01). Lymph node metastasis was an independent prognostic risk factor (P<0.01). CONCLUSIONS In patients with gastric cancer without serosal invasion, lymph node metastasis is an predictive factor regardless it is based on the extent or the number of lymph node metastasis.