Background. Percutaneous coronary intervention (PCI) of unprotected left main coronary artery disease (ULMCAD) have become a feasible and efficient alternative to coronary artery bypass surgery, especially in patients with acute coronary syndrome (ACS). There are limited data regarding early and late outcomes after ULMCAD PCI in patients with ACS and stable angina.The aim of this study was to compare early and four-year clinical outcomes in patients with ULMCAD PCI presenting as ACS or stable angina in a high-volume PCI center.Methods. We conducted a single center retrospective observational study, which included 146 patients with ULMCAD undergoing PCI between 2014 and 2018. Patients were divided in two groups: Group A included patients with stable angina (n = 70, 47.9%) and Group B patients with ACS (n = 76, 52.1%).Results. 30-day mortality was 8.22% overall, lower in Group A (1.43% vs 14.47%, p = 0.02). Mortality and major adverse cardiac events (MACE) rates at 4 years were significantly lower in Group A (9.64% vs 33.25%, p = 0.001, and 24.06% vs 40.11%, p = 0.012, respectively). Target lesion revascularization (TLR) at 4 year did not differ between groups (15% in Group A vs 12.76% in Group B, p = 0.5).Conclusions. In our study patients with ULMCAD and ACS undergoing PCI had higher early and long-term mortality and MACE rates compared to patients with stable angina, with similar TLR rate at 4-year follow-up.