SummaryThis review examines ulcers and gastrointestinal bleeding with low‐dose aspirin, focusing on randomized placebo‐controlled trials.The single endoscopic trial assessing ulcers showed no significant difference in 12‐week ulcer incidence: 6% of 381 given placebo vs. 7% of 387 given 81 mg enteric‐coated aspirin.The relative risk of major gastrointestinal bleeding with low‐dose aspirin in a meta‐analysis of placebo‐controlled trials of vascular protection was 2.07 (95% CI: 1.61–2.66). The absolute rate increase with aspirin above placebo was 0.12% per year (95% CI: 0.07–0.19%) with a number‐needed‐to‐harm of 833 patients (95% CI: 526–1429). A meta‐analysis of aspirin 50–1500 mg daily reported an odds ratio for any gastrointestinal bleeding of 1.68 (95% CI: 1.51–1.88) with an number‐needed‐to‐harm at 1 year of 247. The relative risk of hospitalization for upper gastrointestinal bleeding with low‐dose aspirin in a large Danish cohort study was 2.6 (95% CI: 2.2–2.9) with an absolute annual incidence of 0.6%.Factors that may increase the risk of gastrointestinal bleeding include prior history of ulcers or gastrointestinal bleeding, corticosteroid use, anticoagulant therapy and addition of a non‐aspirin non‐steroidal anti‐inflammatory drug.When determining whether low‐dose aspirin is appropriate for an individual patient, the cardiovascular benefit must be weighed against the potential for clinical events such as gastrointestinal bleeding.