We occurred in a left main (LM) dissection during primary coronary intervention in a 45-year-old man with anterior acute myocardial infarction. Successful, multiple direct stenting was performed from the ostial to the mid left anterior descending coronary artery (LAD). Nonetheless, an LM dissection involving the proximal circumflex artery (Cx) was still evident at the end of the intervention. Multislice Computed Tomography (MSCT) coronary angiography images showed that LM dissection was definitely long and close to the ostium; moreover, the proximal stent had both excluded the false lumen in the LAD and stabilized the dissection towards the Cx. Two months later, at MSCT coronary angiography the LM dissection was still evident and the patient had remained totally asymptomatic. MSCT coronary angiography can be recommended as a complementary diagnostic tool for the assessment of LM anatomy because of the possibility of three-dimensional reconstructions and consequent clear evaluation of its take-off, course and bifurcation.