The SYNTAX (Synergy Between Percutaneous Coronary Intervention with TAXUS and Cardiac Surgery) trial provides the largest randomized dataset from which to assess the early and longer-term safety and efficacy of PCI for left main disease ((3),4). A total of 1,800 patients with 3-vessel and/or left main disease (angiographic stenosis ≥50%) were randomly assigned to PCI with paclitaxel-eluting stents or to CABG; randomization was stratified according to the presence or absence of left main disease. The primary endpoint was MACCE at 1 year, and PCI would be deemed noninferior to CABG if the upper bound of the 95% CI for the absolute risk difference between the 2 strategies was <6.6%. The prespecified statistical analysis plan was to first compare the overall population, with the left main subgroup compared subsequently only if noninferiority was concluded for the overall comparison. PCI was not noninferior to CABG for the prevention of MACCE in the overall trial (17.8% vs. 12.4%) (3), and therefore the findings within the left main cohort must be interpreted as observational and hypothesis-generating only. The trial used a novel method to calculate angiographic complexity, called the SYNTAX score, which incorporates the number of lesions, lesion location, lesion length, the presence of chronic total occlusions, bifurcations or trifurcations, aorto-osital stenoses, vessel tortuosity, calcification, thrombus, and diffuse disease. A higher SYNTAX score reflects greater anatomic complexity. Among the 750 patients in the unprotected left main cohort, the mean EuroSCORE (a measure of surgical risk) was 3.9, the mean SYNTAX score was 30, and slightly more than one-third of the patients had 3-vessel disease in addition to left main obstruction. The 1-year MACCE rates were similar for PCI and CABG (15.8% vs. 13.7%, p = 0.48), with significantly lower rates of repeat revascularization in the patients randomly assigned to CABG (11.8% vs. 6.5%, p = 0.02) at the cost of more strokes (0.3% vs. 2.7%, p = 0.009). In patients with low and intermediate SYNTAX scores (0 to 22 and 23 to 32), 1-year MACCE rates were numerically lower with PCI (7% vs. 13% [p = 0.19]; 12.6% vs. 15.5% [p = 0.54]), whereas in those with SYNTAX scores >32, MACCE rates after CABG were significantly better (25.3% vs. 12.9%, p = 0.008). At the 3-year follow-up, there continued to be no significant difference within the overall left main cohort in the rate of MACCE between treatment strategies (26.8% vs. 22.3%, p = 0.20); repeat revascularization was still more frequent with PCI (20.0% vs. 11.7%, p = 0.004), whereas the risk of stroke after PCI remained lower (1.2% vs. 4.0%, p = 0.02) (Figure 85_gr1) (5). Consistent with the 1-year results, patients with the greatest anatomic complexity (SYNTAX score >32) had inferior outcomes when treated with PCI at 3 years (MACCE rates: 37.3% vs. 21.2%; p = 0.003). With regard to safety, patients randomized to PCI had a numerically lower but not significantly different rate of the composite endpoint of death, myocardial infarction (MI), or stroke (13.0% vs. 14.3%, p = 0.60) and of all-cause death (7.3% vs. 8.4%, p = 0.64). Therefore, within SYNTAX, with the exception of the highest-risk anatomy (SYNTAX score >32), unprotected left main PCI seemed to be as safe as CABG at 3 years, and PCI outcomes were most favorable in the patients with low to intermediate anatomic complexity. Although there are many limitations to the SYNTAX trial, it currently remains the largest RCT comparing PCI with CABG in a prespecified left main subgroup.