Patients with acute coronary syndrome (ACS) are at risk for recurrent adverse events, and multiple reports suggest that this risk is increased in patients with concomitant diabetes mellitus (DM) and peripheral artery disease (PAD). The aim of this article was to investigate cardiovascular outcomes in patients with DM presenting with ACS, stratified by PAD status. Data were derived from 4 randomized post-ACS trials (PLATO [Platelet Inhibition and Patient Outcomes], APPRAISE-2 p Apixaban for Prevention of Acute Ischemic Events 2], TRILOGY [Targeted Platelet Inhibition to Clarify the Optimal Strategy to Medically Manage], and TRACER [Thrombin Receptor Agonist for Clinical Event Reduction in Acute Coronary Syndrome]). Using Cox regression analysis, we investigated major adverse cardiovascular events (MACEs), a composite of cardiovascular mortality, myocardial infarction (MI), or stroke and the individual components of MACE and all-cause mortality in patients with DM, presenting with ACS, stratified by PAD status as the risk modifier. This study included 15,387 patients with a diagnosis of DM and ACS, of whom 1,751 had an additional diagnosis of PAD. PAD was associated with more than doubled rates of MACE (hazard ratio [HR] 2.03, 95% confidence interval [CI] 1.81 to 2.27), all-cause mortality (HR 2.48, 95% CI 2.14 to 2.87), cardiovascular mortality (HR 2.42, 95% CI 2.04 to 2.86), and MI (HR 2.07, 95% CI 1.79 to 2.38). Patients with both PAD and DM were also more optimally treated with antihypertensive, antidiabetic, and statin medication at baseline. In conclusion, this analysis of 4 major post-ACS trials showed that patients with DM and PAD had a substantially higher risk of MACE, cardiovascular mortality, all-cause mortality, and MI despite being optimally treated with guideline-based therapies.