Paula Rodriguez-Miguelez,1 Nichole Seigler,1 Leon Bass,2 Thomas A Dillard,2 Ryan A Harris1,3 1Division of Clinical and Translational Sciences, Georgia Prevention Institute, Georgia Regents University, Augusta, GA, USA; 2Pulmonary and Critical Care Medicine, Department of Medicine, Georgia Regents University, Augusta, GA, USA; 3Sport and Exercise Science Research Institute, University of Ulster, Jordanstown, Northern Ireland, UK Background: Elevated cardiovascular disease risk is observed in patients with COPD. Non-invasive assessments of endothelial dysfunction and arterial stiffness have recently emerged to provide mechanistic insight into cardiovascular disease risk in COPD; however, the reproducibility of endothelial function and arterial stiffness has yet to be investigated in this patient population.Objectives: This study sought to examine the within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD.Methods: Baseline diameter, peak diameter, flow-mediated dilation, augmentation index, augmentation index at 75 beats per minute, and pulse wave velocity were assessed three times in 17 patients with COPD (six males, eleven females, age range 47–75 years old; forced expiratory volume in 1 second =51.5% predicted). Session A and B were separated by 3 hours (within-day), whereas session C was conducted at least 7 days following session B (between-day). Reproducibility was assessed by: 1) paired t-tests, 2) coefficients of variation, 3) coefficients of variation prime, 4) intra-class correlation coefficient, 5) Pearson’s correlations (r), and 6) Bland–Altman plots. Five acceptable assessments were required to confirm reproducibility. Results: Six out of six within-day criteria were met for endothelial function and arterial stiffness outcomes. Six out of six between-day criteria were met for baseline and peak diameter, augmentation index and pulse wave velocity, whereas five out of six criteria were met for flow-mediated dilation. Conclusion: The present study provides evidence for within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD. Keywords: arterial stiffness, endothelial function, flow-mediated dilation, pulse-wave velocity, chronic obstructive pulmonary disease