The prevalence of lower extremity peripheral arterial disease (PAD) varies across populations, based on the groups studied and the detection methods used. The ankle-brachial index (ABI) is a more sensitive tool for PAD detection than is screening for intermittent claudication (IC); only about 10% to 30% of patients diagnosed with PAD based on the ABI have classic symptoms of IC. The prevalence of PAD increases markedly with older age and in persons with diabetes or a history of smoking; prevalence also is elevated in persons with hyperlipidemia, hypertension, or chronic kidney disease. PAD is more prevalent in primary care medical practices than in community-dwelling populations. PAD (defined as an ABI < 0.90) is associated with a twofold to three-fold increased risk of cardiovascular mortality. Borderline and low-normal ABI values, as well as elevated ABI values (> 1.30 or > 1.40), are increasingly recognized as being associated with elevated cardiovascular mortality. Persons with PAD have significantly increased functional impairment and elevated rates of functional decline relative to those without PAD.