Background-High aortic stiffness has been shown to be a strong predictor of morbidity and mortality in the general population and several patient cohorts. However, in patients after ST-elevation myocardial infarction, the prognostic value of high aortic stiffness is unknown so far. Methods and Results-This prospective observational study included 160 consecutive patients with first acute ST-elevation myocardial infarction. Aortic pulse wave velocity (PWV) was measured 2 (interquartile range 2-4 days) days after infarction using cardiac magnetic resonance imaging. The primary end point was defined as a composite end point of major adverse cardiac and cerebrovascular events (MACCE) comprising death, nonfatal myocardial reinfarction, new congestive heart failure, and stroke. During a median follow-up of 1.2 years (interquartile range 1.0-3.1 years), 19 (12%) MACCE events occurred. Kaplan-Meier analysis showed a significantly lower MACCE-free survival in patients with high PWV (PWV > 7.3 m/s, log-rank P=0.003). Multivariable Cox regression analysis revealed PWV > 7.3 m/s to be an independent predictor of MACCE after adjustment for age, sex, mean blood pressure, N-terminal pro-brain natriuretic peptide levels, presence of multivessel disease, and left ventricular stroke volume (hazard ratios >= 3.5; 95% confidence interval 1.4-13.3; all P <= 0.018). In reclassification analysis the addition of PWV to a risk model comprising major clinical prognostic parameters led to a net reclassification improvement of 0.11 (95% confidence interval 0.06-0.17; P < 0.001). Conclusions-Increased aortic stiffness is an independent predictor of MACCE after acute ST-elevation myocardial infarction. Moreover, the assessment of aortic stiffness in addition to classical risk factors significantly improved early risk stratification.