Gastro-esophageal reflux disease encompasses a spectrum of disorders in which gastric reflux leads to symptoms and/or damage to the esophageal mucosa. Although a common problem in clinical practice, our understanding of the pathophysiology of the condition has not been matched by our knowledge of its epidemiology and natural history. This review examines some of the difficulties inherent in epidemiological studies with particular emphasis on the nature and variety of reflux symptoms and their relationship to esophagitis, the natural history and complications of reflux disease, Barrett's esophagus, and the possible role of gastroesophageal reflux in lung disease, especially asthma.