An overview is given of the pathogenic mechanisms involved in Helicobacter pylori-associated duodenal and gastric ulceration. Special attention is given to the role of microbial virulence factors, the effects on gastric acid secretion and the development of 'gastric type' metaplasia in the duodenal bulb. Cure of the infection essentially eliminates ulcer recurrence. Cure also prevents ulcer-related bleeding. Antibiotic regimens providing a reliable high cure rate are briefly discussed. Finally the questions about ulcer disease which remain unanswered are summarized.