The presence of Helicobacter pylori and the gastric mucosa histology were investigated in 15 children and 15 adults with duodenal ulcer. The microorganism was isolated from antral and oxyntic mucosa in 100% of patients, both adults and children. The results of Gram stain and preformed urease test were compared with those of culture and there was no difference in sensitivity among the tests. Antral chronic gastritis was observed in all patients. However, children presented oxyntic gastritis more frequently than adults. It was also observed that the endoscopic aspects were different in the two groups of patients. The results here observed strongly support the idea that, as well as in adults, H. pylori is the causative agent of the gastritis seen in children with duodenal ulceration. On the other hand, the histological findings of oxyntic mucosa of children with duodenal ulcer were different from those of adults.