To compare the use of evidence-based pharmacological and invasive treatments and 12-month mortality rates between patients with and without diabetes who present with acute myocardial infarction (MI), and to explore the relationship between these treatments and late clinical outcomes. Prospective, nationwide multicentre registry: the Acute Coronary Syndrome Prospective Audit (ACACIA). Patients presenting to 24 metropolitan and 15 non-metropolitan hospitals with acute coronary syndrome (ACS) and a final discharge diagnosis of acute MI between November 2005 and July 2007. All-cause mortality at 12 months. Nearly a quarter of 1744 patients with a final diagnosis of acute MI had a history of diabetes on presentation. Patients with diabetes were older, with a greater prevalence of comorbidities than non-diabetic patients, and were less likely to be treated at discharge with evidence-based medications (aspirin, clopidogrel, a statin and/or a beta-blocker) or to receive early invasive procedures. After adjusting for baseline characteristics and therapeutic interventions, diabetes at presentation was independently associated with a higher mortality at 12 months after MI (hazard ratio, 1.79; 95% CI, 1.18-2.72; P=0.007). Early invasive management and discharge prescription of guideline-recommended medications were associated with a significantly reduced hazard of mortality at 12 months. Patients with diabetes have a higher risk than non-diabetic patients of late mortality following an acute MI, yet receive fewer guideline-recommended medications and early invasive procedures. Increased application of proven pharmacotherapies and an early invasive management strategy in patients with diabetes presenting with ACS might improve their outcomes. STUDY PROTOCOL NUMBER (SANOFI-AVENTIS): PML-0051.