Probably all non-steroidal anti-inflammatory drugs (NSAIDs) increase the risk of gastrointestinal (GI) mucosal injury. Not only gastric and duodenal but also oesophageal, small bowel and colonic lesions have been reported. Gastroduodenal lesions are seen most frequently and of these, gastric erosions in the prepyloric region are most prominent. NSAIDs also increase the incidence of peptic ulcers although it is not yet clear whether more gastric or duodenal ulcers are produced. GI symptoms are prevalent during NSAID treatment but there is no correlation between symptoms and lesions. Clinical presentation may, therefore, vary considerably: many symptomatic patients will have no lesions whereas others will present with complications but no symptoms. Blood loss is the most frequent complication of NSAID induced GI lesions. Bleeding is usually silent and occult, the incidence of overt haemorrhage, although rare, is also increased. Other complications such as penetration and perforation may also occur. Endoscopy is the diagnostic method of choice as most mucosal lesions are superficial. However, because of the lack of correlation between symptoms and lesions it is difficult to select patients at risk and to avoid unnecessary procedures. Results of studies performed show that treatment of NSAID induced gastroduodenal lesions with conventional anti-ulcer therapy is probably effective. There are also indications that preventive therapy is effective.