Aspirin (acetylsalicylic acid) and other NSAIDs are responsible for many adverse effects. Among them, pseudo-allergic reactions (urticaria/angioedema, asthma, anaphylaxis) affect up to 9% of the population and up to 30% of asthmatic patients. The mechanisms provoking these reactions have not been fully elucidated, but it appears that inhibition of cyclo-oxygenase (COX) plays a central role. The anti-inflammatory action of nimesulide differs from that of other NSAIDs, possibly because of its chemical structure. In particular, nimesulide is selective for COX-2 and displays additional properties in terms of its effects on inflammatory mediator synthesis and release. For these reasons, nimesulide is generally well tolerated by NSAID-intolerant patients and patients with NSAID-induced asthma. The good tolerability of nimesulide as an alternative drug for use in patients with NSAID intolerance has been demonstrated in a large number of clinical studies.