Given the importance of understanding CLI patients' outcomes and existing gaps in knowledge, there is a pressing need to collect observational data on treatment patterns, adherence to performance measures, and outcomes that are relevant to patients and clinicians. To address this need, the current study will pilot test the research infrastructure and data elements needed to build a larger, national study collecting of the CLI population. It will also provide much-needed preliminary information to identify areas of action that can be targeted in quality improvement programs for this population. Most importantly, it will provide data on health status outcomes in patients with CLI, as a function of individual patient characteristics (demographics, socio-economic and clinical background) and the treatments that patients have undergone. The PORTRAIT-CLI study will also be well equipped to identify potential disparities in the provision of care and patients' outcomes as a function of patient's characteristics.

Inclusion Criteria:

All race/ethnicity categories, English or Spanish speaking, men and women

• Age ≥18 years
• Patients presenting with Rutherford Classification 4 (ischemic rest pain), or Rutherford Classification 5 (minor tissue loss: non-healing ulcer, focal gangrene with diffuse pedal ischemia), or Rutherford Classification 6 (major tissue loss: extending above transmetatarsal level, functional foot no longer salvageable) at specialty clinics will prospectively be screened, regardless of whether the patient undergoes endovascular, bypass, amputation, and/or medical therapy.
• Diagnosis is supported by any of the following hemodynamic parameters (assessed pre- procedurally): Ankle pressure lower than 70 mmHg; Toe pressure lower than 50 mmHg or evidence of ischemia by transcutaneous oxygen measurement (tcpO2) <40 or a skin perfusion pressure (SPP) <40 or angiographic evidence of significant vascular disease

Exclusion Criteria:

• No other prior surgical or vascular interventions within 2 weeks before and/or planned 30 days after the enrollment
• Acute limb ischemia
• Unable to provide written informed consent
• Currently a prisoner

Project coordinators at each recruitment site will have direct access to the PAD clinic schedules and will be prospectively screening from that list. A screening form with limited demographic information will be completed for all patients with a diagnosis of CLI supported by any of the following hemodynamic parameters (assessed pre-procedurally): Ankle pressure lower than 70 mmHg; Toe pressure lower than 50 mmHg or evidence of ischemia by transcutaneous oxygen measurement (tcpO2) <40 or a skin perfusion pressure (SPP) <40 or angiographic evidence of significant vascular disease.