In the absence of a supervisor, we conducted endoscopic submucosal dissection (ESD) procedures using the needle-knife and insulation-tipped (IT) diathermic knives for 516 gastric neoplasms in 443 Japanese patients with the diseases. No significant difference was found between IT knife ESD and needle-knife ESD in en bloc resection rates with tumor-free margins (89.8% and 92.9% for IT knife ESD and needle-knife ESD, respectively) and perforation rates (2.2% and 4.6%, respectively). However, the mean procedure time was significantly (P