Background & Aims There is disagreement over the ideal duration of initial proton pump inhibitor (PPI) therapy for gastroesophageal reflux disease, and whether prolonged therapy increases healing of the esophagitis and prevents symptom relapse. We performed a multicenter, prospective, randomized, controlled study to compare the efficacies of 4 weeks vs 8 weeks of PPI therapy in reducing reflux symptoms and preventing symptom relapse in patients with Los Angeles grade A or B erosive esophagitis. Methods Consecutive patients with symptomatic Los Angeles grade A or B erosive esophagitis were assigned randomly to groups given daily esomeprazole (40 mg) for 4 weeks (n = 207) or 8 weeks (n = 201) as their initial treatment. Patients with complete symptom resolution were switched to on-demand therapy until the end of week 20. All patients underwent follow-up endoscopy at the end of week 20. Symptom relapse was defined as 2 or more episodes of troublesome reflux symptoms per week or ingestion of PPI for more than 7 days within 4 weeks, owing to reflux symptoms. Results The 4-week and 8-week groups had comparable rates of complete symptom resolution (77.9% vs 82.1%). However, the cumulative 12-week incidence of symptom relapse was higher for the 4-week group than for the 8-week group (62.5% vs 47.8%; difference, 14.7%; 95% confidence interval, 3.7%–25.7%; P = .009). No significant difference was observed between groups in the proportions of patients with sustained healing at the end of week 20 (49.6% vs 40.9%; P = .160). Conclusions Prolonging PPI therapy from 4 weeks to 8 weeks does not appear to increase the rate of complete symptom resolution in patients with mild erosive esophagitis. However, 8 weeks of PPI therapy reduces symptom relapse, compared with 4 weeks, in patients with Los Angeles grade A or B erosive esophagitis. ClinicalTrials.gov number: NCT01874535.