The impact of diabetes mellitus (DM) on the outcomes of bifurcation percutaneous coronary intervention (PCI) has received limited study. We compared the procedural characteristics and outcomes of patients with and without diabetes mellitus among 1,302 bifurcation PCIs (1,147 patients) performed at five centers between 2013-2024. The prevalence of diabetes mellitus was 33.8% (n=388). Patients with diabetes were younger, had more cardiovascular risk factors and higher angiographic complexity, including more main vessel calcification and more frequent stenoses in the left main, proximal left anterior descending and right coronary artery. There was no difference in technical (95.5% vs 94.9%, p = 0.613) or procedural success (90.2% vs 91.3%, p = 0.540); provisional stenting was used less frequently in diabetic patients (64.5% vs 71.1%, p = 0.015). Diabetic patients had higher rates of repeat in-hospital PCI and acute kidney injury. Other in-hospital outcomes were similar after adjusting for confounders. During a median follow-up of 1,095 days diabetes was independently associated with higher incidence of major adverse cardiovascular events (hazard ratio [HR]: 2.04, 95% confidence intervals [CI]: 1.52, 2.72, p < 0.001), myocardial infarction (HR: 1.94, 95% CI: 1.05, 3.25, p = 0.033), death (HR: 2.26, 95% CI: 1.46, 3.51, p < 0.001), target (HR: 1.6, 95% CI: 1.01, 2.66, p = 0.045) and non-target (HR: 2.00, CI: 1.06, 3.78, p = 0.032) vessel revascularization. Compared with non-diabetics, patients with diabetes mellitus undergoing bifurcation PCI had higher risk of in-hospital repeat-PCI and major adverse cardiac events during follow-up.Diabetes mellitus (DM) increases the risk of coronary artery disease (CAD) and has been associated with more complex and multifocal coronary lesions (1,2). Percutaneous coronary intervention (PCI) in diabetic patients has been associated with high short- and long-term incidence of adverse events in some (3) but not all (4,5) studies. In a study by Xue et al. newly diagnosed and previously known diabetes patients undergoing PCI had higher incidence of follow-up major adverse cardiac events (MACE) rates compared with non-diabetics (6). Bifurcation lesions account for 15-20% of all PCIs and can be challenging to perform (7-9). Bifurcation PCI has been associated with lower technical and procedural success (10) and higher adverse outcomes (11,12). While there are published data on the impact of diabetes mellitus in patients undergoing PCI (13), there is limited data on its impact on bifurcation PCI (Table 1). We examined the impact of diabetes mellitus on the outcomes of bifurcation PCI in a multicenter registry.