OBJECTIVE Some patients with suspected ST-segment elevation (STE) myocardial infarction (STEMI) show STE that does not fulfill the current criteria for STEMI. The purpose of this study was to investigate the characteristics and prognoses of patients with minimal STEMI. METHODS Between November 2007 and December 2011, 546 patients who underwent primary percutaneous coronary intervention (PCI) for STEMI were enrolled. RESULTS The minimal STE group had a higher proportion of women (30.2 vs. 21.0%, p = 0.031), better pre-PCI antegrade flow (Thrombolysis in Myocardial Infarction flow 2-3, 30.2 vs. 18.8%, p = 0.006) and better collateralization (Rentrop score 2-3, 27.4 vs. 18.1%, p = 0.024) compared to the definite STE group. Multivariate analysis showed that each of them were independent predictors for minimal STE. However, 1-year mortality of the minimal STE group did not differ from that of the definite STE group (7.1 vs. 9.3%, log-rank p = 0.315). CONCLUSIONS Female gender, good collateral flow and good pre-PCI antegrade flow were independent predictors for minimal STE in patients with STEMI. However, minimal STE was not related to a good prognosis in patients with STEMI.