Gastroesophageal reflux is considered to cause sleep disturbance, whereas proton pump inhibitor (PPI) administration is reported to improve insomnia associated with gastroesophageal reflux disease (GERD). The majority of patients with gastroesophageal reflux are asymptomatic and a significant number with erosive esophagitis are also reported to be asymptomatic. We examined whether PPI administration has a therapeutic effect for improving insomnia in patients without reflux symptoms in the same manner as patients with reflux symptoms.We performed a randomized multicenter double-blind placebo-controlled trial using 176 patients with insomnia regardless of the presence of reflux symptoms. The patients were divided into those administered omeprazole (20 mg) or a placebo for 14 days. Four self-reporting questionnaires, QOLRAD-J (Japanese translation of Quality of Life in Reflux and Dyspepsia), Pittsburg Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), and a sleep diary, were used for evaluating GERD-related quality of life (QOL) and sleep disturbance.We evaluated 171 patients with insomnia, of whom 69 had typical reflux symptoms. Omeprazole statistically significantly improved GERD-related QOL from 30.8±0.7 to 33.0±0.5 (P<0.01) (QOLRAD-J, total) and from 6.0±0.2 to 6.6±0.1 (P<0.01) (QOLRAD-J, sleep-related) when administrated to patients with reflux symptoms. Omeprazole also improved insomnia significantly better than the placebo in patients with reflux symptoms; PSQI, from 9.3±0.5 to 7.9±0.5 (P<0.01) and sleep diary, from 2.1±0.1 to 1.8±0.1 (P<0.01). On the other hand, the therapeutic effects of omeprazole and the placebo were not different in patients without reflux symptoms.Our results showed that PPI administration is effective only for insomnia in patients with reflux symptoms.