Helicobacter pylori (H. pylori) infection and non-steroidal anti-inflammatory drugs (NSAIDs) or aspirin induce serious gastrointestinal ulcer and bleeding. Also both H. pylori infection and NSAIDs or aspirin use independently and significantly increase the risk of peptic ulcer and its complications. Interestingly, it has been reported that no evidence exists that reducing the dose or using modified release formulations such as enteric-coated of aspirin would reduce the incidence of ulcer bleeding. Selective COX-2 inhibitors use shows a low relative risk of ulcer bleeding than NSAIDs. However, when combined with aspirin, the differences between selective COX-2 inhibitors and NSAIDs tend to disappear. NSAIDs/aspirin dominantly develops multiple ulcers from the angulus to the antrum regardless of H. pylori infection. In contrast, the irregular shape of ulcer is more frequently detected in patients taking NSAIDs in comparison with H. pylori-associated ulcer, but the association was not seen in cases taking aspirin. This result indicates that the mechanism of ulcer formation may be different between NSAIDs and aspirin.