We report a case of acute coronary syndrome in a patient with suspect Marfan syndrome, 25 days after emergent modified Bentall-De Bono intervention for acute type I peripartum aortic dissection. She was admitted to our intensive care unit because of unstable angina, caused by critical blood flow reduction in a large portion of the myocardium, according to the severity of the symptoms and the electrocardiographic alterations. Coronary angiography showed a sub-occlusive stenosis of the left main coronary artery as a result of the dissection extension to the coronary ostium. Because of the high risk related to heart surgery, the patient was successfully treated by unprotected angioplasty and drug-eluting stent positioning. Short- and mid-term outcomes were favourable. Subsequent tests confirmed the diagnosis of Marfan syndrome. After 2 years of follow-up, the patient remains asymptomatic and in good health. To our knowledge, this is the first report of a successful percutaneous intervention of the left main coronary artery in a patient with Marfan syndrome who had already undergone ascending aortic root and valve replacement by the Bentall-De Bono procedure for acute dissection.