Historical data indicate that approximately 10% of acute coronary syndrome patients have no obstructive coronary artery disease (CAD) but contemporary incidence of non-obstructed coronary arteries in ST-segment elevation myocardial infarction (STEMI) is not clear. We aimed both to identify the contemporary incidence of MI without obstructive CAD (MINOCA)-using the ESC definition-and assess clinical outcomes. We assessed consecutive unselected STEMI patients presenting to the cardiac catheterisation laboratory with a view to undergoing primary percutaneous coronary intervention (PPCI). MINOCA was defined according to ESC criteria. Electronic patient records, blood results, angiographic and echocardiographic data were interrogated to determine final diagnosis, as well as 30-day and 1-year mortality rate. Of 2521 patients with full electronic dataset, 2158 (85.6%) underwent PPCI for obstructive CAD (angiographic stenosis > 70%). A further 167 (6.6%) with obstructive CAD were treated medically or surgically. The remaining 196 (7.8%) patients had absence of obstructive CAD at angiography, of whom 167 had no stenosis (< 30%) and 29 had mild coronary atheroma (stenosis > 30% but < 50%). A total of 110 (4.4%) patients met diagnostic criteria for MINOCA. All-cause mortality at 30-days and 1-year were 3.6% and 4.5%, respectively. In our cohort, 1 in 20 patients presenting with STEMI had MINOCA. This is the first description of the relatively high incidence of MINOCA in a STEMI cohort using current ESC definition and diagnostic criteria and could help power future trials in this area. Mortality rate was relatively high in our study and similar to that in large meta-analyses.