Acetylsalicylic acid is an effective antiplatelet drug for primary and secondary prevention of heart and brain vascular diseases. Analyses of trials including patients with atherosclerosis proved that vascular ischaemic events have been reduced by 25% and risk of vascular death has been reduced due to aspirin. The increasing number of reports about aspirin resistance (the failure of the compound to protect from an ischemic event despite regular intake of appropriate doses) is alarming. The purpose of this review is to present current opinions and results of investigations connected with this problem.