AIMS To describe the incidence of dyspnoea and its associations with demographic characteristics and clinical outcomes in patients with acute coronary syndromes (ACS) treated with ticagrelor or clopidogrel in the PLATelet inhibition and patient Outcomes (PLATO) study. METHODS AND RESULTS In the PLATO study, 18 624 patients were randomized to receive either clopidogrel [300-600 mg loading dose (LD), 75 mg daily] or ticagrelor (180 mg LD, 90 mg b.i.d.). The occurrence of reported dyspnoea adverse events (AEs) was analysed in the 18 421 patients who received at least one dose of study medication in relation to demographic characteristics, clinical outcomes and other associations of patients with and without dyspnoea. A total of 1339 ticagrelor-treated patients (14.5%) and 798 clopidogrel-treated patients (8.7%) had a dyspnoea AE following randomization, with respectively 39 (0.4%) and 24 (0.3%) classified as severe in intensity. Excluding dyspnoea AEs occurring after the secondary endpoint of myocardial infarction (MI), the yearly rates of the efficacy endpoints in dyspnoea AE patients in the ticagrelor and clopidogrel groups were: for the primary composite of CV death, MI, and stroke, 8.8 and 10.4% (unadjusted P = 0.25; adjusted P = 0.54); for CV death, 3.1 and 4.8% (unadjusted P = 0.024; adjusted P = 0.18); and for total death 3.7 and 6.2% (unadjusted P = 0.004; adjusted P = 0.06), respectively. CONCLUSIONS Ticagrelor-related dyspnoea is usually mild or moderate in intensity and does not appear to be associated with differences concerning any efficacy or safety outcomes with ticagrelor compared with clopidogrel therapy in ACS patients.