Observational studies report poor prognosis of patients after acute coronary syndrome (ACS) in the presence of previous peripheral arterial disease (PAD), but data on subclinical PAD are scarce. This study was designed to assess the predictive value of clinical and subclinical PAD in the follow-up of patients after an ACS. We included 1,054 patients hospitalized for an ACS who survived the acute phase. Patients were divided into 3 groups: clinical PAD (previously diagnosed PAD or intermittent claudication), subclinical PAD (defined as ankle-brachial index <or=0.9 or >1.4), and no PAD. Clinical PAD was present in 150 patients (14.2%) and 298 cases of subclinical PAD were detected (28.3%). Patients with PAD (clinical and subclinical PAD) were significantly older and had a higher prevalence of hypertension and diabetes mellitus than those without PAD. During the 1-year follow-up, 59 patients died (5.6%). Previous PAD (hazard ratio 4.38, 95% confidence interval 1.96 to 9.82, p <0.001) and subclinical PAD (hazard ratio 2.35, 95% confidence interval 1.05 to 5.23, p <0.05) were associated with increased cardiovascular mortality. Moreover, patients with clinical PAD had higher rates of major cardiovascular events (myocardial infarction, angina, and heart failure) than patients with subclinical PAD or without PAD. In conclusion, beyond clinical PAD, measurement of ankle-brachial index after ACS provides substantial information on intermediate-term prognosis.