BACKGROUND & AIMS:Agents are being developed for treatment of eosinophilic esophagitis (EoE). However, it is not clear what outcome measures would best determine the efficacy and safety of these agents in clinical trials. We performed a systematic review of outcomes used in randomized placebo-controlled trials of EoE and we estimate the placebo response and rates of remission. METHODS:We searched MEDLINE, Embase, CENTRAL, ClinicalTrials.gov, and the EU Clinical Trials Register from inception through February 20, 2018 for randomized controlled trials of pharmacologic therapies for EoE. Efficacy outcome definitions, measurement tools, and the proportion of patients responding to placebo were collected and stratified by based on histologic, endoscopic, and patient-reported outcomes. RESULTS:We analyzed data from 22 placebo-controlled trials, comprising 1112 patients with EoE. Ten additional active registered trials were identified. Most published trials evaluated topical corticosteroid therapy (13/22, 59.1%). Histologic outcomes measuring eosinophil density and patient-reported outcomes were reported in 21/22 published trials (95.5%). No consistently applied definitions of histologic or patient-reported response or remission were identified. Endoscopic outcomes were described in 60% (12/20) of published trials. The EoE Endoscopic Reference Score is the most commonly applied tool for describing changes in endoscopic appearance. The median histologic response to placebo was 3.7% (range, 0%-31.6%) and the median rate of remission in patients given placebo was 0.0% (range, 0%-11.0%). The median patient-reported response to placebo was 14.4% (range, 8.6%-77.8%) and rate of remission in patients given placebo was 26.2% (range, 13.2%-35.7%). CONCLUSIONS:In a systematic review of the literature, we found that no standardized definitions of histologic, endoscopic, or patient-reported outcomes are used to determine whether pharmacologic agents produce a response or remission in patients with EoE. A core outcome set is needed to reduce heterogeneity in outcome reporting and facilitate trial interpretation and comparison of results from trials.