Peroral endoscopic myotomy (POEM) is becoming the treatment of choice for achalasia. Data beyond 3 years are emerging but are limited. We herein report our 10-year experience, focusing on long-term efficacy and safety including the prevalence, management, and sequelae of postoperative reflux. This was a single-center prospective cohort study. Six hundred ten consecutive patients received POEM from October 2009 to October 2019, 160 for type 1 achalasia (26.2%), 307 for type II (50.3%), 93 for type III (15.6%), 25 for untyped achalasia (4.1%), and 23 for nonachalasia disorders (3.8%). Two hundred ninety-two patients (47.9%) had prior treatment(s). There was no aborted POEM. Median operation time was 54 minutes. Accidental mucosotomies occurred in 64 patients (10.5%) and clinically significant adverse events in 21 patients (3.4%). No adverse events led to death, surgery, interventional radiology interventions/drains, or altered functional status. At a median follow-up of 30 months, 29 failures occurred, defined as postoperative Eckardt score >3 or need for additional treatment. The Kaplan-Meier clinical success estimates at years 1, 2, 3, 4, 5, 6, and 7 were 98%, 96%, 96%, 94%, 92%, 91%, and 91%, respectively. These are highly accurate estimates because only 13 patients (2%) were missing follow-up assessments. One hundred twenty-five patients (20.5%) had reflux symptoms more than once per week. At a median of 4 months, the pH study was completed in 406 patients (66.6%) and was positive in 232 (57.1%), and endoscopy was completed in 438 patients (71.8%) and showed reflux esophagitis in 218 (49.8%), mostly mild. POEM is exceptionally safe and highly effective on long-term follow-up, with >90% clinical success at ≥5 years.