Abstract Aim Frailty is associated with adverse outcomes in older patients with acute coronary syndrome (ACS). The impact of frailty on long-term clinical outcomes following invasive management of non-ST elevation ACS (NSTEACS) is unknown. Methods and results The multi-centre Improve Clinical Outcomes in high-risk patieNts with ACS 1 (ICON-1) prospective cohort study consisted of patients aged >75 years undergoing coronary angiography following NSTEACS. Patients were categorized by frailty assessed by Canadian Study of Health and Ageing Clinical Frailty Scale (CFS) and Fried criteria. The primary composite endpoint was all-cause mortality, unplanned revascularization, myocardial infarction, stroke, and bleeding. Of 263 patients, 33 (12.5%) were frail, 152 (57.8%) were pre-frail, and 78 (29.7%) were robust according to CFS. By Fried criteria, 70 patients (26.6%, mean age 82.1 years) were frail, 147 (55.9%, mean age 81.3 years) were pre-frail, and 46 (17.5%, mean age 79.9 years) were robust. The composite endpoint was more common at 5 years among patients with frailty according to CFS (frail: 22, 66.7%; pre-frail: 81, 53.3%; robust: 27, 34.6%, P = 0.003), with a similar trend when using Fried criteria (frail: 39, 55.7%; pre-frail: 72, 49.0%; robust: 16, 34.8%, P = 0.085). Frailty measured with both CFS and Fried criteria was associated with the primary endpoint [age and sex-adjusted hazard ratio (HR) compared with robust groups. CFS: 2.22, 95% confidence interval (CI) 1.23–4.02, P = 0.008; Fried: HR 1.81, 95% CI 1.00–3.27, P = 0.048]. Conclusion In older patients who underwent angiography following NSTEACS, frailty is associated with an increased risk of the primary composite endpoint at 5 years. Registration: Clinicaltrials.gov NCT01933581