Gastroesophageal reflux disease (GERD) produces a spectrum of symptoms ranging from mild to severe. While the role of the lower esophageal sphincter in the pathogenesis of GERD has been studied extensively, less attention has been paid to esophageal peristalsis, even though peristalsis governs esophageal acid clearance. The aim of this study was to evaluate the following in patients with GERD: (1) the nature of esophageal peristalsis and (2) the relationship between esophageal peristalsis and gastroesophageal reflux, mucosal injury, and symptoms. One thousand six consecutive patients with GERD confirmed by 24-hour pH monitoring were divided into three groups based on the character of esophageal peristalsis as shown by esophageal manometry: (1) normal peristalsis (normal amplitude, duration, and velocity of peristaltic waves); (2) ineffective esophageal motility (IEM; distal esophageal amplitude < 30 mm Hg or >30% simultaneous waves); and (3) nonspecific esophageal motility disorder (NSEMD; motor dysfunction intermediate between the other two groups). Peristalsis was classified as normal in 563 patients (56%), IEM in 216 patients (21%), and NSEMD in 227 patients (23%). Patients with abnormal peristalsis had worse reflux and slower esophageal acid clearance. Heartburn, respiratory symptoms, and mucosal injury were all more severe in patients with IEM. These data show that esophageal peristalsis was severely impaired (IEM) in 21% of patients with GERD, and this group had more severe reflux, slower acid clearance, worse mucosal injury, and more frequent respiratory symptoms. We conclude that esophageal manometry and pH monitoring can be used to stage the severity of GERD, and this, in turn, should help identify those who would benefit most from surgical treatment.