BACKGROUND AND AIM: Several studies performed in Western countries demonstrate the association between sleep dysfunction and gastroesophageal reflux disease (GERD), especially when nighttime heartburn is present. The purpose of this study was to examine the prevalence and risk factors of sleep dysfunction, and the effect of rabeprazole on reflux symptoms and sleep dysfunction in Japanese GERD patients. METHODS: A total of 134 GERD patients, including 82 patients with non-erosive reflux disease (NERD), were enrolled. Patients received rabeprazole 10 mg daily for 8 weeks. Patients were asked to complete both a frequency scale for symptoms of GERD (FSSG) questionnaire and a Pittsburgh Sleep Quality Index (PSQI) questionnaire at baseline and 8 weeks after treatment. RESULTS: Sleep dysfunction defined as a PSQI score >5.5 was found in 70 (52.2%) of the GERD patients. NERD was significantly associated with sleep dysfunction compared to erosive reflux disease (OR 2.18, 95% CI 1.05-4.53). However, other factors, including nighttime heartburn, were not associated with sleep dysfunction. Rabeprazole treatment significantly decreased both the FSSG and the PSQI score. CONCLUSION: The prevalence of sleep dysfunction was high among GERD patients. NERD was identified as a risk factor for sleep dysfunction. Use of a proton-pump inhibitor led to an effective decrease in sleep dysfunction. These results suggest a different pathogenesis of sleep dysfunction in Japanese GERD patients compared to GERD patients in Western countries. However, acid plays an important role in sleep dysfunction in all patients with GERD.