AIM: To evaluate the effectiveness of endoscopic submucosal dissection using an insulation-tipped diathermic knife (IT-ESD) for the treatment of patients with over 20 mm early gastric cancer (EGC). METHODS: A total of 112 patients with over 10 mm EGC were treated with IT-ESD at Sumitomo Besshi Hospital and Shikoku Cancer Center in the 5 year period from January 2002 to December 2006, including 40 patients with over 20 mm EGC. We compared patient backgrounds, the one-piece resection rate, complete resection (CR) rate, operation time, bleeding rate, perforation rate between patients with over 20 mm EGC [over 20 mm group (21-40 mm)] and the remaining patients (under 20 mm group). RESULTS: We found no significant difference in the rate of underlying cardiopulmonary disease (over 20 mm group vs under 20 mm group, 5.0% vs 5.6%), one- piece resection rate (95% vs 96%), CR rate (85% vs 89%), operation time (72.3 min vs 66.5 min), bleeding rate (5% vs 4.2%), and perforation rate (0% vs 1.4%) between the 2 groups. Three patients in each group had submucosal invasion and two in each groups underwent additional surgery. CONCLUSION: There was no significant difference in the outcome resulting from IT-ESD between the 2 groups. Our study proves that IT-ESD is a feasible treatment for patients with over 20 mm mucosal gastric cancer although the long-term outcome should be evaluated in the future. AIM: To evaluate the effectiveness of endoscopic submucosal dissection using an insulation-tipped diathermic knife (IT-ESD) for the treatment of patients with over 20 mm early gastric cancer (EGC). METHODS: A total of 112 patients with over 10 mm EGC were treated with IT-ESD at Sumitomo Besshi Hospital and Shikoku Cancer Center in the 5 year period from January 2002 to December 2006, including 40 patients with over 20 mm EGC. We compared patient backgrounds, the one-piece resection rate, complete resection ( CR) rate, operation time, bleeding rate, perforation rate between patients with over 20 mm EGC [over 20 mm group (21-40 mm)] and the remaining patients (under 20 mm group) the rate of the underlying cardiopulmonary disease (over 20 mm group vs under 20 mm group, 5.0% vs 5.6%), one-piece resection rate (95% vs 96%), CR rate 72.3 min vs 66.5 min), bleeding rate (5% vs 4.2%), and perforation rate (0% vs 1.4%) be tween the 2 groups. Three patients in each group had submucosal invasion and two in each groups underwent additional surgery. CONCLUSION: There was no significant difference in the outcome therefrom from IT-ESD between the 2 groups. Our study proves that IT-ESD is a feasible treatment for patients with over 20 mm mucosal gastric cancer the long-term outcome should be evaluated in the future.