Determination of the exact prevalence of gastroesophageal reflux (GER) and GER disease (GERD) at any age is virtually impossible mainly because symptoms are not specifc, not all patients seek medical help, many patients are not (fully) investigated, and prospective data are limited. Many epidemiologic studies evaluated in infancy the frequency of regurgitation which is a common physiologic symptom in the frst months of life with a spontaneous recovery in nearly all infant. Many other esophageal and extraesophageal symptoms and signs of GER(D) have been reported, but sensitivity and specifcity are low, the causal relation is uncertain, and there is a lack of diagnostic gold standard technique. While reflux occurs physiologically at all ages, there is also a continuum between physiologic GER and GERD leading to different manifestations and complications depending on individual sensitivity and perception, defense mechanisms, mucosal resistance, and possible genetic influence. In selected population such as children with neurological impairment, cystic fbrosis, and esophageal atresia, severe persisting GER and esophageal complications have been frequently reported. Whether early treatment of GER(D) signifcantly changes, the incidence or severity of symptoms and complications in adults is uncertain.