Gastroduodenitis is a gastroenterological disease in which the inflammatory process affects the mucous membranes of two organs: the stomach and duodenum. The prevalence of this pathology is extremely high and can compete with the prevalence of gastritis. Gastroduodenitis can occur both in childhood and in adults. Late referral to a specialist or an incorrectly selected treatment pattern leads to the development of complications such as pancreatitis, enterocolitis, gastric ulcer or duodenal ulcer. Often against the background of gastroduodenitis, dysbiosis develops.