Background Peroral endoscopic myotomy (POEM) is a novel, minimally invasive treatment for esophageal achalasia. We retrospectively examined and evaluated the results following POEM to verify the technique’s efficacy and safety. Methods We retrospectively analyzed data for patients who underwent POEM at eight Japanese facilities between September 2008 and October 2015. Pre- and postoperative assessments 3 months and 1 year after POEM included patient interviews, endoscopy, and manometry. Results A total of 1346 patients underwent POEM during the study period. Achalasia was the straight type in 1105 patients (82%) and the sigmoid type in 241 patients (18%). The average patient age was 47.2 years (range 3–95 years); 617 patients (46%) were men and 729 (54%) were women. Previous treatment included balloon dilatation in 381 patients (28%) and Heller–Dor operation in 43 patients (3%). The average operation time was 99.6 min. The mean length of the myotomy in the esophageal body was 10.8 cm, and the myotomy extended into the stomach a mean of 2.8 cm. The response rate (Eckardt score ≤ 3) was 95.1% 3 months postoperatively and 94.7% 1 year postoperatively. We noted 50 adverse events (3.7%) of Clavien–Dindo classification grade ≤ IIIa, and all resolved with conservative treatment. There were no Clavien–Dindo classification grade ≥ IIIb adverse events. After POEM, erosive esophagitis according to the Los Angeles classification was absent in 37% of the patients, grade A in 33%, B in 24%, C in 6%, and D in 0.2%. Symptomatic gastroesophageal reflux disease after POEM was confirmed in 14.8% of the patients; both erosive esophagitis and symptomatic gastroesophageal reflux disease responded to treatment with a proton-pump inhibitor. Conclusion Our results confirmed the safety and efficacy of POEM in a large patient series and support POEM as the first-line and standard treatment for esophageal achalasia.