Previous studies analyzing the relation between time-to-reperfusion, infarct size, microvascular obstruction (MO) and infarct transmurality in patients with ST-elevation myocardial infarction (STEMI) reperfused by primary percutaneous coronary intervention (PCI) reported inconsistent results. Furthermore, it remains unclear, if transmural infarction is associated with adverse clinical outcome. The present study included STEMI patients reperfused by primary PCI (n = 322) within 720 min after symptom-onset undergoing contrast-enhanced magnetic resonance imaging (CMR) at a median of 3 days after the index event [interquartile range (IQR) 2-4]. Patients were subcategorized into tertiles according to time-to-reperfusion. Infarct size and MO were assessed approximately 15 min after gadolinium-injection. Infarct transmurality was assessed by a score with late-enhancement grading as <25, 25-50, 51-75 and >75% transmurality analyzing all 17 left ventricular segments. Clinical follow-up was performed after 20 months (IQR 13;29). The primary endpoint was defined as a composite of death and congestive heart failure. The median time-to-reperfusion was 230 min (IQR 153;390). Infarct size and MO did not increase significantly with longer time-to-reperfusion (p = 0.16 and p = 0.44, respectively). In contrast to infarct size and MO, the infarct transmurality score progressed significantly with increasing ischemic time (p < 0.001). In multivariable logistic regression analysis, time-to-reperfusion was identified as an independent predictor for transmural infarction (p = 0.03). However, transmural infarction was not predictive of the primary composite clinical endpoint (p = 0.22). In conclusion, in STEMI patients reperfused by primary PCI, time-to-reperfusion was an independent predictor for transmural infarction but not for infarct size and MO. However, transmural infarction was not predictive of death and congestive heart failure.