['To evaluate the role of Helicobacter pylori infection and other clinical factors in the risk of upper gastrointestinal bleeding in patients taking low-dose aspirin.', 'A case-control study was carried out of consecutive current users of low-dose aspirin admitted because of upper gastrointestinal bleeding. Within a cohort of 695 patients with upper gastrointestinal bleeding, 98 patients had taken low-dose aspirin and no other non-steroidal anti-inflammatory drug. Controls were 147 low-dose aspirin users without upper gastrointestinal bleeding of similar age, sex and extent of aspirin use as cases. H. pylori infection was determined by CagA/VacA serology and 13C-urea breath test in all cases and controls. Adjusted odds ratios (OR) are provided.', 'H. pylori infection was identified as an independent risk factor of upper gastrointestinal bleeding in this population (OR, 4.7; 95% confidence interval (95% CI), 2.0-10.9), but the presence of CagA-positive serology was not. Other risk factors identified were a previous ulcer history (OR, 15.2; 95% CI, 3.8-60.1), alcohol use (OR, 4.2; 95% CI, 1.7-10.4) and use of calcium channel blockers (OR, 2.54; 95% CI, 1.25-5.14). Antisecretory therapy (OR, 0.1; 95% CI, 0.02-0.3) and nitrovasodilators (OR, 0.2; 95% CI, 0.1-0.6) decreased the risk of bleeding.'] Does helicobacter pylori increase the risk of upper gastrointestinal bleeding in patients taking low-dose aspirin?