Abstract Background and aims Cardiovascular magnetic resonance (CMR) comprehensively assesses aortic stiffness and myocardial ischemia in a single examination. Aortic stiffness represents a subclinical marker of cardiovascular risk in the general population, including patients with diabetes mellitus. However, there is no prognostic data regarding aortic stiffness in patients with diabetes mellitus undergoing stress perfusion CMR. Methods Consecutive patients with diabetes mellitus with suspected myocardial ischemia referred for adenosine stress perfusion CMR with aortic pulse wave velocity (PWV) during 2010–2013 were studied. The primary outcome was major adverse cardiovascular events (MACE), defined as the composite of cardiac mortality, nonfatal myocardial infarction (MI), hospitalization for heart failure, coronary revascularization (> 90 days post-CMR), and ischemic stroke. The secondary outcome was hard cardiac events, defined as the composite of cardiac mortality and nonfatal MI. Results A total of 424 patients (median follow-up 7.2 years) were included. The mean PWV was 12.16 ± 6.28 m/s. MACE and hard cardiac events occurred in 26.8% and 9.4% of patients, respectively. Patients with elevated PWV (> 12.16 m/s) had a significantly higher incidence of MACE (HR 2.14 [95%CI 1.48, 3.09], p < 0.001) and hard cardiac events (HR 2.69 [95%CI 1.42, 5.10], p = 0.002) compared to those with non-elevated PWV. Multivariable analysis demonstrated that PWV independently predicts MACE (p = 0.003) and hard cardiac events (p = 0.01). Addition of PWV provided incremental prognostic value beyond clinical data, left ventricular mass index, myocardial ischemia, and late gadolinium enhancement in predicting MACE (incremental χ² 7.54, p = 0.006) and hard cardiac events (incremental χ² 5.99, p = 0.01). Conclusions Aortic stiffness measured by CMR independently predicts MACE and hard cardiac events and confers significant incremental prognostic value in patients with diabetes mellitus with suspected myocardial ischemia. Aortic stiffness measurement could potentially be considered as part of a stress perfusion CMR protocol to enhance risk prediction in patients with diabetes mellitus.