Purpose: Different definitions of periprocedural myocardial infarction (MI) after Percutaneous Coronary Intervention (PCI) have been provided, but their impact on prognosis remains to be determined. Methods: All consecutive patients undergoing PCI in Our Institution from 2009 to 2011 were enrolled. Procedural data were revised to adjudicate diagnosis of periprocedural myocardial infarction according to CK-MB increase (>3 x URL and>5 x URL), to troponin increase (>3 x 99th percentile URL and >5 x 99th percentile URL) and to recent ESC and SCAI definitions. MACE (Major Adverse Cardiovascular events) was the primary end point, while its single components (death, myocardial infarction and target vessel revascularization) the secondary ones. Results: 712 patients were enrolled: after 771 days, 115 (16.7%) patients experienced MACE 190 patients were diagnosed a periprocedural MI defined as elevation of troponin >5x99th percentile URL. When adjudicating ESC definition on these patients, 46 were excluded and 1.4% of them experienced a MACE and 0.3% died, while among 144 with periprocedural MI, 2.9% reported a MACE and 1.3% died. After appraisal of SCAI definition, 176 patients were excluded, 3.8% of them with a MACE and 1.4% died, and for those with periprocedural MI, 0.5% experienced a MACE and 0.1% died. Similar low performance was appraised after reclassification of patients from more than 3 of upper limit of CK-MB and of troponin. At multivariate analysis, none of these definitions related to adverse events. Conclusions: Periprocedural MI represents a frequent complication for patients undergoing PCI. Al present definitions share a still not satisfactory discrimination between patients with and without adverse events at follow up, stressing the need for more accurate definitions.