The risk factors, typical symptoms (intermittent claudication, critical limb ischaemia) and treatment of peripheral arterial disease (PAD) are widely studied and well-known to clinicians. The role of elevated ankle-brachial index (ABI) in the process of diagnosing PAD and the prevalence and clinical features of PAD in nonagenarians are, however, unknown. In addition, the relationship between PAD and functional decline has attracted little attention until recently. We therefore began to pursue more knowledge about factors underlying or indicating PAD in older people and to describe functional decline in peripheral arterial disease. The association of elevated ABI and PAD was assessed in a clinical sample of 1,762 patients admitted to the vascular outpatient clinic by comparing the ABI and TBI results, in addition to determining further which factors were significantly associated with PAD among those with elevated ABI. The role of PAD among nonagenarians was evaluated in a cohort of 90-year-old individuals (N=58) by measuring ABI and inquiring about their mobility level. In a subgroup of participants, lower extremity functional status was measured by performing walking tests. The association of PAD and mortality among nonagenarians was also assessed during a one-year follow-up. The relationship between PAD and impaired balance was evaluated both cross-sectionally and longitudinally by using standardized force platform balance tests. The results of two population-based studies (The Evergreen project [N=419] and the Health 2000 survey [N=1323]) were analyzed for this purpose. The prevalence of elevated ABI among patients admitted to the vascular outpatient clinic was 8.4% and that of PAD among them 62%–84% depending on the cut-off value (1.3¬¬–1.5). PAD was significantly more probable among those with chronic renal failure, a history of smoking and coronary heart disease (CHD). The specificity of elevated ABI (≥ 1.3) in identifying patients with PAD seems to be good, whereas its sensitivity in excluding the disease is only satisfactory. Among nonagenarians, PAD was mainly asymptomatic, with a prevalence of 22%. Moreover, approximately one third of them presented with elevated ABI. Nonagenarians with a low (<0.9) or high (>1.4) ABI reported more difficulties in the physical activities of daily living (PADL tasks) than those with normal ABI, but the results did not reach statistical significance. Furthermore, an abnormal ABI was shown to correlate with poorer one-year survival among the subjects. The results also implied that PAD is associated with poorer balance performance both cross-sectionally and longitudinally. In the cross-sectional analysis, the presence of diabetes exacerbated the deterioration in balance but alone affected balance somewhat less than PAD. The utility of ABI in diagnosing PAD seems to be more wide-ranging than the traditional conception presumes. In addition, PAD, even though mainly asymptomatic, continues to affect the life of nonagenarians. However, more studies are required to determine the possible relationship between PAD and mobility loss in very old people. The fact that PAD is associated with poorer balance gives the clinician a tool for recognizing those possibly at greater risk for mobility loss and nursing home placement.