Peroral endoscopic myotomy (POEM) is a safe and effective minimally invasive treatment for achalasia. Postoperative reflux rates remain high. The functional luminal imaging probe (FLIP) allows intraoperative measurement of lower esophageal distensibility during POEM. In theory, this enables a tailoring of myotomies to ensure adequate distensibility while minimizing postoperative reflux risk. Two prospectively collected POEM databases were analyzed from two UK tertiary upper GI centers. The operators in each center used FLIP measurements to ensure adequate myotomy. Outcome measures included Eckardt score (where <3 indicated clinical success) and proton-pump inhibitor use (PPI), collected at the first postoperative appointment. Length of stay was recorded as were complications. In all, 142 patients underwent POEM between 2015 and 2019. Overall, 90% (128/142) had postoperative Eckardt scores of <3 at 6 weeks. Clinical success improved to 93% (66/71) in the latter half of each series with a significantly higher rate of complete symptom resolution (53 versus 26%, P = 0.003). In all, 79% of the poor responders had previous interventions compared with 55% of responders (P = 0.09). Median post-myotomy distensibility index was 4.0 mm2/mmHg in responders and 2.9 in nonresponders (P = 0.16). Myotomy length of <7 cm was associated with 93% clinical success and 40% post op PPI use compared with 60% PPI use with longer myotomies. There were two type IIIa, two type IIIb, and one IV Clavien-Dindo complications. This is the largest series of endoluminal functional lumen imaging probe (EndoFLIP)-tailored POEM in the UK to date. The shorter myotomies, allowed through EndoFLIP tailoring, remained clinically effective at 6 weeks. Complete symptom response rates improved in the latter half of each series. More data will be needed from high-volume collaborations to decipher optimal myotomy profiles based on EndoFLIP parameters. © The Author(s) 2022. Published by Oxford University Press on behalf of International Society for Diseases of the Esophagus. All rights reserved. For permissions, please e-mail: [email protected].