Background: Endoscopic submucosal dissection (ESD) is less invasive than surgical resection, but the large mucosal defects after ESD may lead to adverse events necessitating hospitalizations. Objective: To evaluate the use of an endoscopic suturing device for closure of large mucosal defects after ESD. Design and Setting: Retrospective, single-center study. Patients: Twelve consecutive patients underwent ESD. Interventions: All lesions were removed by using a previously described ESD technique. The large mucosal defects post-ESD were completely closed with the endoscopic suturing device, and all patients were discharged home with subsequent clinical and endoscopic follow-up. Main Outcome Measurements: Bleeding and perforation rates after ESD with mucosal defect closure. Results: ESD followed by endoscopic suturing of the mucosal defects was performed in 12 patients ( mean age, 64.7 +/- 11.2 years, 4 lesions in the stomach, 8 lesions in the colon; mean lesion size, 42.5 +/- 14.8 mm) over a period of 8 months. All lesions (100%) were removed en bloc. Closure of post-ESD defects with an endoscopic suturing device was technically feasible and fast (mean closure time, 10.0 +/- 5.8 minutes per patient). Only 1 stitch (continuous suturing line) was required for complete closure in 8 patients. In the other 4 patients, the mucosal defect was closed with 2 to 4 separate stitches (mean number of sutures per patient, 1.6 +/- 1.0). There were no immediate or delayed adverse events in any of the study patients. Limitations: Retrospective study. Conclusions: Closure of large post-ESD defects with the Overstitch endoscopic suturing device is technically feasible and fast and can significantly decrease treatment cost by eliminating the need for hospitalization.