We examined the effect of cilostazol, a type III phosphodiesterase inhibitor, on pain-free and maximal walking distance and quality of life measures. The present study examined adverse effects in 2,702 patients with stable, moderate to severe claudication enrolled in 8 randomized, double-blind, placebo-controlled trials. Treatment duration ranged from 12 to 24 weeks. Cilostazol therapy increased maximal and pain-free walking distances by 50% and 67%, respectively. In subgroup analysis, cilostazol increased pain-free and maximal walking distance similarly in men and women, in older (>/=65 years) and younger patients, and in patients with and without diabetes. Quality-of-life assessments revealed enhanced scores for physical well-being. Cilostazol-treated patients reported a higher incidence of headache, bowel complaints, and palpitations than patients given placebos. Cilostazol decreased triglycerides by 15.8% and increased high-density lipoprotein cholesterol by 12.8%, but there were no deleterious effects on any hematologic or serum markers. We conclude that cilostazol significantly increases walking distance and quality-of-life measures in patients with claudication without major adverse effects.