Subclinical peripheral artery disease (PAD) might be associated with pathophysiology of contrast-induced acute kidney injury (CI-AKI). We hypothesized that concomitant PAD in patients with the acute coronary syndrome (ACS) would represent a high-risk subgroup with a greater incidence of CI-AKI, both of which lead to higher mortality after percutaneous coronary intervention (PCI). Six hundred and seventy-five consecutive patients with ACS who underwent PCI and examination of ankle-brachial index (ABI) were analyzed retrospectively. The presence of PAD was defined as an ABI < 0.9. We investigated whether (1) PAD was an independent predictor of CI-AKI (≥ 0.3 mg/dL or ≥ 50% relative increase in serum creatinine within 48 h after PCI) and (2) PAD and CI-AKI were independently associated with long-term mortality. Of the 675 patients with ACS, 114 (17%) exhibited PAD. The incidence of CI-AKI was significantly higher in PAD patients, compared with the remaining patients (12% vs. 4%, p < 0.001). Multivariate logistic regression analysis revealed that the presence of PAD was an independent predictor for the development of CI-AKI [odds ratio 2.50, 95% confidence interval (CI) 1.07–5.73, p < 0.05]. During the median 4-year follow-up, there were 65 incidents of all-cause death. In the multivariate Cox proportional hazard regression analysis, the presence of PAD [hazard ratio (HR) 2.08, 95% CI 1.17–3.65, p < 0.05] and CI-AKI (HR 2.23, 95% CI 1.08–4.26, p < 0.05) were associated with an increased risk of all-cause mortality. Assessment of ABI provides useful information for predicting CI-AKI and long-term mortality in patients with ACS after PCI.