Bivalirudin demonstrated similar efficacy but resulted in a lower rate of bleeding compared to unfractionated heparin (UFH) plus platelet glycoprotein IIb/IIIa inhibitors in patients undergoing percutaneous coronary intervention. It has not been clearly evaluated whether this can also be applied to patients with diabetes mellitus. A total of 335 consecutive patients with diabetes mellitus referred for elective percutaneous coronary intervention were randomized in the Novel Approaches for Preventing or Limiting EventS (NAPLES) trial to receive bivalirudin monotherapy or UFH plus routine tirofiban. The primary composite end point (30-day composite incidence of death, urgent repeat revascularization, myocardial infarction, and all bleeding) was lower in the bivalirudin group than in the UFH plus tirofiban group (18.0% vs 31.5%, odds ratio 0.47, 95% confidence interval 0.28 to 0.79, p = 0.004). No death, urgent revascularization, or Q-wave myocardial infarction occurred. The rate of non-Q-wave myocardial infarction was similar in the 2 groups (10.2% in the bivalirudin group vs 12.5% in the UFH plus tirofiban group, p = 0.606). In contrast, fewer patients in the bivalirudin group experienced bleeding (8.4% vs 20.8%, odds ratio 0.34, 95% confidence interval 0.18 to 0.67, p = 0.002). This difference was mainly ascribed to the lower rate of minor bleeding (7.8% in the bivalirudin group vs 18.5% in the UFH plus tirofiban group, odds ratio 0.37, 95% confidence interval 0.19 to 0.74, p = 0.005), although the rate of major bleeding in the 2 groups was comparable (0.6% vs 2.4%, respectively; p = 0.371). In conclusion, in patients with diabetes mellitus undergoing elective percutaneous coronary intervention, the strategy of bivalirudin monotherapy compared to UFH plus routine tirofiban is safe and feasible and associated with a significant reduction of in-hospital bleeding.