To assess the risk of upper gastrointestinal bleeding associated with the use of individual non-narcotic analgesics and non-steroidal anti-inflammatory drugs (NSAIDs), a multicentre study of 875 cases of upper gastrointestinal bleeding and 2682 hospital controls was done. With control for confounding factors, the overall odds ratio estimate for aspirin taken at least once during the week before the first symptom was 7.2 (95% confidence interval 5.4-9.6). Non-aspirin NSAIDs associated with upper gastrointestinal bleeding were diclofenac (7.9 [4.3-14.6]), indomethacin (4.9 [2.0-12.2]), naproxen (6.5 [2.2-19.6]), and piroxicam (19.1 [8.2-44.3]). Paracetamol, propyphenazone, and dipyrone did not increase the risk. A previous history of gastrointestinal bleeding or peptic ulcer did not greatly affect odds ratio estimates, which differed according to sex and were higher for younger than for older patients. However, the incidence of upper gastrointestinal bleeding was higher among the elderly.