Summary Background:  There is an increasing interest in the use of non‐invasive methods for the detection of subclinical atherosclerosis to better identify patients with high risk of cardiovascular events The presence of diabetes mellitus (DM) and peripheral arterial disease (PAD) is associated with increased risk of events but their value in the acute coronary syndrome (ACS) patient has not been ascertained. Methods:  We performed a subanalysis of the PAMISCA study, designed to investigate the prevalence of PAD in patients admitted to Spanish hospitals with a diagnosis of an ACS. Results:  A total of 1410 patients were analysed (71.4% men, age 66 ± 11.9 years, 35% DM). The prevalence of PAD was higher in DM vs. no‐DM (41.5% vs. 30.6% respectively, p < 0.001). Patients with PAD and DM had more in‐hospital cardiac complications such as atrial fibrillation/flutter, recurrent myocardial ischaemia and heart failure and a trend towards higher in‐hospital mortality (p = 0.08). Non‐DM patients with PAD and DM without PAD shared similar cardiac complications and the group without neither PAD nor DM had the best prognosis. In patients without PAD, DM was an independent predictor of three‐vessel coronary disease (OR 1.6; 95% CI: 1.1–2.5, p < 0.05) after adjustment by age, sex, low density lipoproteins (LDL), smoking and the previous myocardial infarction. However, in PAD patients, DM failed to be an independent risk factor in the multivariate analysis (OR 1.0; 95% CI 0.6–1.6, p < 0.05). Conclusions:  The concurrence of DM and PAD helps identify patients with an adverse risk profile.