Endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) is an effective alternative treatment for early gastric cancer. However, a major concern is the likelihood of lymph node metastasis. From December 1987 to December 2006, 391 patients who underwent curative surgery for gastric cancer with mucosal (T1a, n = 265) or submucosal (T1b, n = 126) invasion and a retrieved lymph node number ≧ 15 were enrolled. The frequency and risk factors of lymph node metastasis were analyzed. The frequency of lymph node metastasis was 4.9 % in T1a lesions and 21.4 % in T1b lesions. Although the depth of submucosal tumor invasion was < 2 mm, there was a 28.6 % chance of lymph node metastasis. A T1b lesion, i.e., the width of the submucosal tumor invasion was < 5 mm, resulted in fewer lymph node metastases than lesions > 5 mm in width. Multivariate analysis demonstrated that Lauren's diffuse type and lymphatic invasion were independent risk factors for lymph node metastasis in T1a lesions, while lymphatic invasion was the strongest risk factor for lymph node metastasis in T1b lesions. EMR/ESD is a good alternative for T1a intestinal type adenocarcinoma without lymphatic invasion. Surgical resection is necessary for patients with T1b gastric cancer with lymphatic invasion.