Conventional non steroidal anti-inflammatory drugs (NSAIDs) are probably responsible for a fifth to a quarter of cases of peptic ulcer bleeding, and for the same proportion of deaths. Predisposing factors include age, due probably to underlying susceptibility to ulcer, drug dosage, and the nature of NSAID. It is also likely that prior ulcer predisposes, but whether Helicobacter pylori infection without ulcer does so is unclear. Factors underlying the proportion of ulcer complications not associated causally with NSAID or aspirin treatment, two-third of cases, are largely unknown.