Background: The impact of diabetes mellitus (DM) on angiographic restenosis and clinical outcomes after implantation of drug-eluting stents (DESs) in patients with long coronary lesions (lesion length ���25mm and stent length ���32 mm) has not been investigated. Methods: This study consisted of 166 patients (group I) who had DM and 334 patients (group II) who did not who underwent DES implantation. We compared the incidence of 6-month angiographic restenosis and 9-month major adverse cardiac events (MACEs), defined as cardiac death, myocardial infarction (MI), and target lesion revascularization (TLR), between patients with and without DM. Results: The lesion length (34.5짹11.6 mm in group I vs. 33.9짹12.4 mm in group II, p=0.620) and stent length (41.5짹16.9 mm vs. 39.7짹16.8 mm, p=0.316) were similar between two groups. Reference vessel size was larger in group II than group I (2.74짹0.41 mm in group II vs. 2.87짹0.49 mm in group II, p=0.006). The 6-month angiographic study was performed in 85.5% of group I and 81.7% of group II. The angiographic restenosis rate (9.2% vs 8.8%, p = 0.902) and late loss (0.48짹0.53 mm in group I vs. 0.38짹0.47 mm in group II, p=0.055) (table1) were similar between patients with and without DM. During 9-month follow-up, death (0.6% vs. 0.3%, p=1.0) and TLR (4.8% vs. 4.8%, p=0.989) were similar between two groups. In addition, incidences of MACEs (13.9% in group I vs. 14.1% in group II, p = 0.948) was also similar between two groups. Conclusion: In the era of DES, the presence of DM did not affect angiographic and clinical outcomes in patients with long coronary lesions.