Nighttime reflux during sleep plays a crucial role in several conditions associated with gastroesophageal reflux disease (GERD). Reflux patterns during arousal and sleep are different because of delayed gastric emptying, reduced esophageal peristalsis, decreases in swallowing and salivary secretion, and prolonged esophageal clearance during sleep. Clinical evidence strongly suggests that GERD is associated with sleep disturbances such as shorter sleep duration, difficulty falling asleep, arousals during sleep, poor sleep quality, and awakening early in the morning. New mechanisms on how GERD affects sleep have been recently identified by using actigraphy, and sleep deprivation was found to induce esophageal hyperalgesia to acid perfusion. Thus, the relationship between GERD and sleep disturbances is bidirectional. Among lifestyle modifications, avoidance of a late night meal plays a role in prevention of nighttime reflux. Treatment with a proton pump inhibitor (PPI) improves both nighttime symptoms and subjective sleep parameters, but its effects on objective sleep parameters remain unclear. Better control of nighttime acid secretion by administering a PPI at different times or by providing a double-dose PPI, adding H 2 receptor antagonists, or other new agents is proposed. The effects of such treatments on sleep disturbances remain to be elucidated. GERD patients with sleep disturbances report more severe symptoms and poorer quality of life as compared to those without sleep disturbances. Consequently, GERD should also be classified as GERD with sleep disturbance and GERD without sleep disturbance.