Aspirin (ASA) and nonsteroidal anti-inflammatory drugs (NSAIDs) share common pharmacologic effects in the prevention of inflammation, at least in part through inhibition of prostaglandin formation. ASA and NSAIDs have predictable side effects such as gastric pain, ecchymosis, and tinnitus. They also cause anaphylactoid shock, urticaria/angioedema, nephropathy, and hepatitis in individuals who appear to be normal and in whom prediction of such reactions cannot be made. Two selected populations of patients are likely to experience hypersensitivity reactions to both ASA and NSAIDs. Patients with asthma have an 8% to 20% chance of experiencing asthmatic attacks after ingesting ASA and NSAID. If such patients have associated rhinosinusitis (polyps), prevalence increases to 30% to 40%. Patients with chronic urticaria/angioedema have a 21% to 30% chance of experiencing an urticarial flare after ingesting ASA and NSAIDs.