Purpose: Endoscopic resection is widely accepted as standard treatment for early gastric cancer (EGC) without lymph node metastasis. The procedure is minimally invasive, safe, and convenient. However, surgery is sometimes needed after endoscopic mucosal resection (EMR)/endoscopic submucosal dissection (ESD) due to perforation, bleeding, or incomplete resection. We evaluated the role of surgery after incomplete resection. Materials and Methods: We retrospectively studied 29 patients with gastric cancer who underwent a gastrectomy after incomplete EMR/ESD from 2006 to 2010 at Korea University Hospital. Results: There were 13 incomplete resection cases, seven bleeding cases, three metachronous lesion cases, three recurrence cases, two perforation cases, and one lymphatic invasion case. Among the incomplete resection cases, a positive vertical margin was found in 10, a positive lateral margin in two, and a positive vertical and lateral margin in one case. Most cases (9/13) were diagnosed as mucosal tumors by endoscopic ultrasonography, but only three cases were confirmed as mucosal tumors on final pathology. The positive residual tumor rate was two of 13. The lymph node metastasis rate was three of 13. All lymph node metastasis cases were submucosal tumors with positive lymphatic invasion and no residual tumor in the gastrectomy specimen. No cases of recurrence were observed after curative resection. Conclusions: A gastrectomy is required for patients with incomplete resection following EMR/ESD due to the risk of residual tumor and lymph node metastasis.