Helicobacter pylori was sought prospectively by culture of antral biopsy, histology and serology (IgG and IgA) in 440 consecutive endoscopies on children to determine the prevalence, clinical presentation and histological features of H. pylori infection in our population. Twenty-eight patients had H. pylori (8% overall). The mean age of infected patients was significantly higher than that of non-infected patients (P less than 0.0001). No patient under 5 years of age had H. pylori isolated. Overall, there was no significant difference in clinical presentation between those with and those without H. pylori infection, but 23% of patients 5 and 26 years of age who presented with abdominal pain as the indication for their endoscopy had H. pylori isolated. Macroscopic changes ranged from no abnormality to frank ulceration, but the typical antral mamilliform changes were 100% predictive of infection. Fifty-eight per cent of patients with duodenal ulcers, but only 17% with gastric ulcers had H. pylori infection. Histological gastritis was present in 144 patients (including all H. pylori positive patients). None of the patients with another definable cause for gastritis had H. pylori isolated. In conclusion, H. pylori is an important cause of primary gastritis in our population, occurring in children over 5 years of age. Culture of an antral biopsy should be performed in children over this age undergoing endoscopy for the investigation of abdominal pain and, more particularly, in those with peptic ulceration.