The authors describe lesions of the upper alimentary tract in 91 children aged 4 to 15 years suffering from pyelonephritis. Intragastric pH-metry, endoscopy and histological examination of biopsy specimens from the gastric and duodenal mucosa were carried out, as a result of which gastroduodenal pathology was diagnosed in 3/4 of the patients. In 69.4% of the children, biopsy specimens of the mucous membrane of the antrum of the stomach showed Campylobacter pylori. Such combined pathology requires, in addition to the treatment of pyelonephritis correction of the diet, administration of agents that may contribute to the decrease of upper alimentary tract inflammation. If Campylobacter pylori are detected, the treatment eliminating those bacteria is to be administered.