The introduction of selective inhibitors of cyclo-oxygenase-2 to the marketplace has been much anticipated for several years. It would appear that these compounds have lived up to the expectations of having reduced gastrointestinal toxicity and, at least for some indications, of efficacy similar to that of conventional non-steroidal anti-inflammatory drugs. However, there is a growing body of evidence suggesting that cyclo-oxygenase-2 plays a very important role in gastrointestinal mucosal defence, particularly in situations in which the mucosa is damaged or inflamed. Moreover, physiological roles for cyclo-oxygenase-2 both in the renal and cardiovascular systems are becoming better recognized. Inhibition of cyclo-oxygenase-2 can lead to peripheral oedema and hypertension, and may promote thrombosis. Indeed, there is recent evidence of increased rates of myocardial infarction in arthritis patients taking a selective cyclo-oxygenase-2 inhibitor. Use of low-dose aspirin concurrently with use of a selective cyclo-oxygenase-2 inhibitor may provide some degree of protection against the potential cardiovascular toxicity of the latter but both laboratory and clinical studies suggest that the concomitant use of these two types of drugs results in gastrointestinal ulceration comparable to what is seen with conventional non-steroidal anti-inflammatory drugs. These recent results suggest that care must be exercised in the use of selective cyclo-oxygenase-2 inhibitors by individuals who are at increased risk of myocardial infarction and stroke, and the use of low-dose aspirin by these patients may place them at increased risk of gastrointestinal complications.