The SYNTAX (SX) score, an interesting tool to characterize the severity of the coronary artery disease was designed to predict cardiovascular outcomes in patients with three-vessel or unprotected left main coronary artery (ULMCA) disease in the SYNTAX study. However, the prognostic value of SX score in patients undergoing percutaneous coronary intervention (PCI) of ULMCA stenosis needs to be validated in the “real world”. The aim of our study was to evaluate the clinical outcome of all the patients undergoing PCI for ULMCA stenosis according to the SX score in a monocentric registry. Forty-five patients with de novo ULMCA stenosis (mean age 72 ± 10 years; 76% of male) underwent PCI with bare metal stent (BMS) or drug eluting stent (DES) from January 2006 to December 2008 and were included in the ALMA ( A ngioplasty of L eft M ain at l A riboisière hospital) registry. Twenty nine percent of patients were diabetics, mean ejection fraction (EF) was 54 ± 10%. EuroSCORE value was 5.4 ± 3.2 and SX score was 22 ± 8. Ostial ULMCA stenosis was involved in 27% and distal ULMCA lesion in 62% of cases. Distal ULMCA stenoses were treated by provisional T stenting in most of the cases, with one stent implantation in 48% of patients and with two stents in 44%. Clinical follow-up was achieved in all patients (25 ± 10 months). In-hospital MACCE occurred in 6.7% of patients (2 death and 1 myocardial infarction). The rate of major adverse cardiac or cerebrovascular events (MACCE) was 35.6%. Cardiac mortality in the registry was 8.8% at two years. Target lesion revascularisation occurred in 15.6% of patients (7.1% in the DES group vs. 19.4% in the BMS group; p = 0.31). None of the patients showing restenosis died. SX score was correlated to MACCE and cardiovascular death. A higher SX score (≥33) compared to the lower group (SX score between 0 to 32) is significantly associated with MACCE (83,3% vs. 28,1%; p < 0.01) and cardiac mortality (33.3% vs. 7.7%; p = 0.04). The SX score is a useful tool to predict MACCE and cardiac mortality in patients undergoing percutaneous revascularization of the left main coronary artery.