Background: When acute aortic dissection is complicated with acute myocardial infarction, the diagnosis of dissection can be problematic. In these cases, patients might be treated with primary percutaneous coronary intervention (PCI) and suffer acatastrophic outcome. However, there are few reports or algorithm to facilitate the accurate management of this clinical situation. Methods: We evaluated 385 consecutive patients who underwent primary PCI arising from an initial diagnosis of STEMI at our hospitalbetween January 2006 and March 2011. Clinical characteristics, coronary angiographic findings, and outcomes were obtained from medical charts and databases. Results: Five patients (1.3%) with STEMI secondary to aortic dissection were identified. All patients (100%) had sudden-onset of chest pain and a history of hypertension without diabetes or hyperlipidemia. An increased resistance while advancing the diagnostic catheter was reported by the operators in 3 of 5 patients (60%). Aortography performed by manual contrast-medium injection showed the discrepancy in the diameter between the aortic root and the ascending aorta in 4 patients (100%), and ascending aortic intimal flap dissections were noted in 3 patients (75%). Alternating appearance and disappearance of the coronary artery ostium was observed in 2 patients, and bedside echocardiography showed intimal flap extension inall 4 patients (100%) who underwent this examination. The mortality rate at 30days was 40%. Conclusions: We construct an algorithm that incorporated factors including careful history evaluation, bedside echocardiography, resistance encountered while advancing a catheter, and findings of aortography performed with manual injection,which could b evaluable for this clinical situation.