AIM: The aim of this study was to assess the effect of ticagrelor monotherapy among high-risk patients with anaemia undergoing percutaneous coronary intervention (PCI). METHODS AND RESULTS: In the TWILIGHT (Ticagrelor with Aspirin or Alone in High-Risk Patients after Coronary Intervention) trial, after 3 months of ticagrelor plus aspirin, high-risk patients were maintained on ticagrelor and randomized to aspirin or placebo for 1 year. Anaemia was defined as haemoglobin <13 g/dL for men and <12 g/dL for women. The primary endpoint was Bleeding Academic Research Consortium (BARC) 2, 3, or 5 bleeding. The key secondary endpoint was a composite of all-cause death, myocardial infarction, or stroke.Out of 6828 patients, 1329 (19.5%) had anaemia and were more likely to have comorbidities, multivessel disease, and to experience bleeding or ischaemic complications than non-anaemic patients. Among anaemic patients, BARC 2, 3, or 5 bleeding occurred less frequently with ticagrelor monotherapy than with ticagrelor plus aspirin [6.4% vs. 10.7%; hazard ratio (HR) 0.60; 95% confidence interval (CI) 0.41-0.88; P = 0.009]; the rate of the key secondary endpoint was similar in the two arms (5.2% vs. 4.8%; HR 1.07; 95% CI 0.66-1.74; P = 0.779). These effects were consistent in patients without anaemia (interaction P values 0.671 and 0.835, respectively). CONCLUSION: In high-risk patients undergoing PCI, ticagrelor monotherapy after 3 months of ticagrelor-based dual antiplatelet therapy was associated with a reduced risk of clinically relevant bleeding without any increase in ischaemic events irrespective of anaemia status (TWILIGHT: NCT02270242).