Specimens obtained at gastric biopsies performed for suspected acid peptic disease in patients 5 through 17 years of age were retrospectively reviewed for the presence of Campylobacter pylori (CP), a gram-negative bacillus associated with chronic gastritis and peptic ulcer disease in adults. Of 98 patients who underwent antral biopsy (the most reliably colonized site in the stomach), 40 had chronic gastritis histologically. Of those 40 patients, 22 (55%) had CP present on the gastric surface. None of the 58 patients without gastritis present in biopsy specimens had CP. The gastritis in children with CP was more severe than in those without the organism: 86% of those with moderate gastritis and 92% of those with severe gastritis had CP. Eight patients with duodenal ulcers and one patient with a gastric ulcer had CP on biopsy. Among those patients without CP, only one had a duodenal ulcer and eight had gastric ulcers. An additional nine patients found to have CP on gastric fundic biopsy were identified, for a total of 31 patients with CP identified by either antral (22) or fundic (nine) biopsy. Initial resolution of symptoms with standard acid-antagonist therapy was noted in the 25 of 31 CP(+) patients so treated, but a high relapse rate was noted within one to two years in the patients who also had gastritis and duodenal ulcer. These findings support a strong association between CP colonization of the stomach and the presence of chronic gastritis and duodenal ulcer disease in children.