Our aim was to evaluate the incremental predictive value of adding mean platelet volume (MPV) to the Global Registry of Acute Coronary Events (GRACE) risk score. The MPV and GRACE score were determined on admission in 509 consecutive patients with acute coronary syndrome (ACS). Six-month mortality or nonfatal myocardial infarction (MI) was the study end point. Overall, 61 (12%) patients reached the combined end point. Cox multivariate analysis showed that an elevated MPV was an independent predictor of 6-month mortality or MI in patients with ACS. The addition of MPV to the GRACE model improved its global fit and discriminatory capacity. The new model including MPV allowed adequate reclassification of 16% of the patients. In conclusion, the inclusion of MPV into the GRACE risk score could allow improved risk classification, thereby refining risk stratification of patients with ACS.