As many as 10 million people in the USA have peripheral arterial disease (PAD) with a prevalence over 10% in people aged more than 60 years old. Generally, men have a higher prevalence of PAD than women. The risk factors for PAD are similar to those for coronary artery disease (CAD) and cerebrovascular disease (CBVD), but diabetes and cigarette smoking have a particularly strong association with PAD. Patients with PAD also have CAD and CBVD as co-morbidities, although the extent of co-morbidity depends on the sensitivity of assessment. The risk of mortality is proportional to the severity of PAD, and the relative risk of all-cause mortality due to PAD is unaltered by the presence of CAD or CBVD. PAD is under-recognized and under-treated, even though it should be regarded as a severe disease leading to significant death and disability from stroke and myocardial infarction (MI). Thus, accurate diagnosis of PAD could provide an early indication of the need for intervention and help prevent future morbidity and mortality.