The purposes of this study were to (1) determine if peripheral arterial disease (PAD) severity is related to deficits in lower extremity functional strength, (2) identify covariates that might affect the relationship between lower extremity functional strength and severity of PAD, and (3) determine if the relationship between lower extremity functional strength and severity of PAD still persists after statistically controlling for significant covariates. A total of 144 patients were grouped into tertiles according to disease severity. Patients having an ankle-brachial index (ABI) of 0.76 to 0.90 were classified as having mild PAD (high ABI group), 0.51 to 0.75 classified as having moderate PAD (moderate ABI group), and 0.36 to 0.50 as having severe PAD (low ABI group). Lower extremity functional strength was assessed using the chair-stand test where the time to complete 5 consecutive stand-to-sit transfers was recorded. Patients were also characterized on ambulatory function and clinical characteristics. The moderate ABI group took significantly (p<0.05) less time (13.49 ±0.49 s) to complete the chair-stand test than the low ABI group (15.86 ±0.63 s). Both daily physical activity level and total 6-minute walk distance were identified as significant covariates (p<0.05) of lower extremity functional strength. After controlling for daily physical activity level and total 6-minute walk distance, no significant differences (p>0.05) in the time to complete the chair-stand test existed between the ABI groups. These findings indicate that the greater impairment in lower extremity functional strength in patients with severe PAD is explained by their lower physical activity level and poorer overall walking ability.