Gastroesophageal reflux is an important problem in children for several reasons. It occurs frequently; sometimes features perplexing and misleading symptoms; causes significant morbidity; and defies rapid, simple, and curative therapy. Thus, it is an important disorder for pediatricians to understand. Definitions Gastroesophageal reflux is the return of gastric contents into the esophagus. Confusion sometimes has resulted from failure to distinguish between gastroesophageal reflux as a single event and as a condition, as well as from failure to distinguish between a physiologic and a pathologic condition. A gastroesophageal reflux episode is a single instance of return of gastric contents into the esophagus. Confusion between this single event and the pathologic condition of gastroesophageal reflux disease has been perpetuated by the habit of diagnosing "gastroesophageal reflux" (meaning gastroesophageal reflux disease) on the basis of a single episode of reflux seen on a barium fluoroscopic study or during scintigraphic evaluation. It is important to understand that virtually all people reflux occasionally. The distinction between this physiologic gastroesophageal reflux and pathogenic gastroesophageal reflux (ie, gastroesophageal reflux disease) can be made either by demonstrating an abnormal quantity of reflux (increased frequency or duration of episodes compared to asymptomatic individuals) or by demonstrating that detrimental effects (such as malnutrition, esophagitis, or respiratory disease) have resulted from reflux.