Objectives and background: The aims of this study were to develop a test of competence in endovascular aortic repair (EVAR) stent graft sizing and selection; to examine the test for evidence of validity; and to explore the experience required for the task. Methods: The test was developed based on a literature review resulting in 22 anatomical assessment points and a graft selection. Validity evidence was explored in an international cross sectional study. Twenty-two consultants with varying levels of experience in the field (novices, intermediates, and experts) were presented with computed tomography angiography of the aortic vessels from three patients. Test scores were based on summed z-scores using the anatomical measurements and graft choices of the experts as a reference. A proficiency score was established using the contrasting groups standard setting method. Results: The assessment was shown to be reliable with an intraclass correlation coefficient of 0.83 (p <. .001) and high internal consistency with a Cronbach's α of .91 (p <. .001). Mann-Whitney U test showed that experts performed significantly better than novices and intermediates (p <. .002 and p <. .005, respectively). Regarding anatomical measurements, Mann-Whitney U test could discriminate between experts and novices (p = .002), between experts and intermediates (p = .010), and between novices and intermediates (p = .036). In stent selection the experts performed significantly better than both the novices and the intermediates (p = .002 and p = .007, respectively), while there was no significant difference between the two non-expert groups (p = 1). A credible passing standard with appropriate consequences was established using the contrasting groups methods. Conclusion: This study presents a standardised and objective assessment tool of competence in vessel analysis and stent graft selection for endovascular aortic repair. This was supported by strong validity evidence with good internal consistency and discriminatory ability. The tool may be used to facilitate training and certification of future endovascular specialists.