Critical limb ischemia (CLI) is a severe obstruction of the arteries that seriously decreases blood flow to the extremities resulting in amputation of the affected limb if left untreated. Despite the severity of the disease, there is a lack of data on prevalence, incidence and outcomes of CLI in the United States. OBJECTIVES: We conducted a large population-based study to directly estimate prevalence, incidence and outcomes of CLI in the United States. METHODS: Data from January 2006 to December 2008 were extracted from the U.S. Medicare dataset. We estimated 1) age, gender, race and diabetes-specific CLI prevalence and incidence rates using the direct standardization method, and 2) factors associated with occurrence of outcomes (leg revascularization, non-traumatic amputation, and mortality) among the CLI population, using the Cox proportional hazard regression model. RESULTS: A total of 68,074 patients were identified with eligible CLI ICD-9 codes in 2007 of whom 44.53% were diabetic. Analyzing 2 years of data, CLI prevalence and annual incidence rates in this elderly population were 0.23% (0.28% for male and 0.20% for female patients) and 0.20% (0.23% and 0.17%), respectively. Just as with prevalence, incidence increased sharply among beneficiaries aged 65-69 (0.13%) to ≥85 (0.31%), was around 2.3 times higher in black patients compared to white patients, and 8.6 times higher in diabetic patients compared to non-diabetic patients. The overall incidence rates of leg revascularization and non-traumatic amputation in the year after CLI diagnosis were 29.7% and 25.2%, respectively. Compared to revascularization, patients who are older, male, black, and have diabetes had a higher probability of amputation. 30.3% of the patients died within the first year after CLI diagnosis. CONCLUSIONS: This first U.S. nationwide-based study shows that prevalence, incidence and outcomes are different according to patients’ socio-demographic characteristics and comorbidities, suggesting that CLI patient management varies among the U.S. population.