Zenker's diverticulum (ZD) is the most common type of diverticulum in the esophagus. The endoscopic septotomy of the diverticular wall has become a widely accepted treatment modality, but the recurrence rate is unclear. Our aim was to assess short-term and long-term success rates after flexible endoscopic septotomy for the treatment of ZD. All consecutive patients treated at our department for a ZD between November 2014 and September 2018 were included. Endoscopic septotomy was conducted using a diverticuloscope or a distal attachment cap. Data were retrospectively analyzed from a prospectively collected database. We collected data concerning patients, endoscopic procedures, and short-term clinical outcomes. All patients were reached by phone between October and December 2018 to assess long-term results. Seventy-seven patients were referred to our department for a ZD. Sixty patients were treated using a diverticuloscope and 17 patients with a distal attachment cap. For all 77 patients, the myotomy was technically successful. Three patients treated with a diverticuloscope reported complications. Initial treatment success was 93%. After a mean (±SEM) follow up of 23±2months, 66% of patients had persistent clinical remission. The rate of long-term treatment success was 72% in treatment-naïve and 50% in previously treated patients (P=0.13). Treatment success was 68% in patients treated with the diverticuloscope versus 60% in the group treated with a cap (P=0.75). The flexible endoscopic septotomy for the treatment of ZD is a safe and effective treatment of ZD, with or without a diverticuloscope.