Aspirin resistance refers to less than expected suppression of thromboxane A(2) production by aspirin and has been reported to be independently associated with an increased risk of adverse cardiovascular events. Possible causes of aspirin resistance include poor compliance, drug interaction, inadequate aspirin dose, increase turnover of platelets, genetic polymorphisms of cyclo-oxygenase-1, and upregulation of alternate (non-platelet) pathways of thromboxane production. Laboratory methods used to detect aspirin resistance include those that measure thromboxane A(2) production and thromboxane A(2)-dependent platelet function. However, since there is currently no standardised approach to the diagnosis and there are no proven effective treatments for aspirin resistance that improve outcome, patients with cardiovascular disease receiving aspirin should not be routinely tested for aspirin resistance. Instead physicians should be aware of the factors that may impair aspirin function, ensure that they use an appropriate dose of aspirin and optimise compliance with aspirin therapy. Further research exploring the mechanisms of aspirin resistance is needed in order to better define and develop a standardised test for aspirin resistance that is specific, reliable, can be readily applied in routine laboratories and correlate with an increased risk of cardiovascular events.