We carefully ascertained deaths for a cohort of 744 patients who had undergone noninvasive testing for lower extremity peripheral arterial disease (PAD) in a university affiliated, community hospital. Using a ratio of the ankle and brachial blood pressures (ABI) of less than 0.85 as the criteria, the relative risk (RR) for total mortality associated with PAD was 2.36 (95% CL = 1.60, 3.48) after adjusting for baseline covariates in a proportional hazards model. There was a strong trend for increasing risk with decreasing ABI (P less than 0.0001). Specific causes of death for which survival was directly related to the magnitude of ABI were myocardial infarctions, and deaths other than vascular disease and cancer. There was no relationship between ABI and the risk of mortality from cancer. The mortality experience of those with normal ABI was very similar to that of the general U.S. population (age adjusted RR = 1.14, 95% CL = 0.78, 1.61), whereas the risk for those with an ABI less than 0.4 was markedly elevated in comparison to the U.S. population (RR = 4.49, 95% CL = 3.52, 5.64). Our results suggest that the relatively technically simple measure of the ratio of ankle to brachial blood pressures, if low, carries a very poor prognosis and should prompt investigation and treatment of atherosclerotic disease in other vascular systems.