Introduction: Coronary artery disease (CAD) and peripheral arterial disease (PAD) share the same pathophysiology, but whether the angiographic extent of CAD predicts an abnormal ABPI in a Coronary Care Unit (CCU) setting has not been evaluated. Objectives: We examined for associations between angiographic CAD severity and abnormal ABPI, suggesting the presence of PAD. Methods: We performed a prospective consecutive observational series involving patients admitted to CCU and undergoing coronary angiography. Patients with unmeasurable ABPI or pre-existing PAD were excluded. The ABPI was performed by trained clinical staff and an ABPI ≤ 0.90 was taken as abnormal, which was analysed against the severity of CAD. Angiographic severity >70% stenosis in any major vessel, or previous coronary revascularisation was taken as significant CAD. Results: 82 patients were recruited between August and December 2018. The prevalence of an abnormal ABPI was similar in those with normal coronary arteries and those with any degree of coronary disease: 1 of 8 (12.50%) with normal coronaries had abnormal ABPI versus 12 of 74 (16.21%) of those with coronary disease (p = 0.785). When assessing for a relationship between significant CAD and abnormal ABPI there was none seen; out of 21 patients with no significant CAD (none or mild disease), 3 had abnormal ABPI (14.28%), compared with 10 of 61 patients with significant CAD (16.39%) (p = 0.820). Similarly, there was no association between double and triple vessel CAD and abnormal ABPI. Conclusion: Despite the shared pathophysiology, severity of CAD does not predict an abnormal ABPI in this clinical setting.