ABSTRACT: This study describes the development and psychometric evaluation of a novel patient-reported single-item mobility measure.Prospective cohort study.Four Veteran's Administration Medical Centers.Individuals undergoing their first major unilateral lower extremity amputation; 198 met inclusion criteria; of these, 113 (57%) enrolled.None.The Amputee Single Item Mobility Measure, a single item measure with scores ranging from 0 to 6, was developed by an expert panel, and concurrently administered with the Locomotor Capabilities Index-5 (LCI-5) and other outcome measures at six weeks, four months, and 12 months post-amputation. Criterion and construct validity, responsiveness, and floor/ceiling effects were evaluated. Responsiveness was assessed using the standardized response mean.The overall mean 12-month Amputee Single Item Mobility Measure score was 3.39?±1.4. Scores for transmetatarsal, transtibial, and transfemoral amputees were 4.2 (±1.3), 3.2 (±1.5), and 2.9 (±1.1), respectively. Amputee Single Item Mobility Measure scores demonstrated "large" and statistically significant correlations with the LCI-5 scores at six weeks (r?=?0.72), four months (r?=?0.81), and 12 months (r?=?0.86). At four months and 12?months, the correlation between Amputee Single Item Mobility Measure scores and hours of prosthetic use were r?=?0.69 and r?=?0.66, respectively, and between Amputee Single Item Mobility Measure scores and Trinity Amputation and Prosthesis Experience Scales functional restriction scores were r?=?0.45 and r?=?0.67, respectively. Amputee Single Item Mobility Measure scores increased significantly from six weeks to 12?months post-amputation. Minimal floor/ceiling effects were demonstrated.In the unilateral dysvascular amputee, the Amputee Single Item Mobility Measure has strong criterion and construct validity, excellent responsiveness, and does not exhibit floor/ceiling effects.