We sought to determine whether diabetes mellitus independently conferred poor prognosis in patients with acute myocardial infarction (AMI) undergoing primary percutaneous coronary intervention (PCI). In 3,742 patients enrolled in the Primary Angioplasty in Myocardial Infarction (PAMI) studies with the intention of undergoing primary PCI, we compared in-hospital mortality, 6-month mortality, and 6-month major adverse cardiovascular events (MACEs), i.e., composite of death, reinfarction, or ischemic target vessel revascularization (TVR), between diabetics (n = 626, 17%) and nondiabetics (n = 3,116, 83%). We evaluated the independent impact of diabetes on outcomes after adjustment for baseline clinical and angiographic differences. Diabetics had worse baseline clinical characteristics, longer pain onset-to-hospital arrival time, and longer door-to-balloon time. They had more multivessel coronary disease and lower left ventricular ejection fractions, but better baseline Thrombolysis In Myocardial Infarction (TIMI) flow. Diabetics underwent primary PCI less often (88% vs 91%, p = 0.01). During the index hospitalization, diabetics were more likely to die (4.6% vs 2.6%, p = 0.005). During 6-month follow-up, diabetics had higher incidences of death (8.1% vs 4.2%, p <0.0001) and MACEs (18% vs 14%, p = 0.036). In multivariate analysis, diabetes was independently associated with 6-month mortality (hazard ratio 1.53, 95% confidence interval 1.03 to 2.26, p = 0.03), but not with in-hospital mortality or 6-month MACEs. We conclude that diabetics with AMI have less favorable baseline characteristics and are less likely to undergo primary PCI than nondiabetics. Despite excellent angiographic results, diabetics had significantly worse 6-month mortality.