Fine-needle aspiration (FNA) guided by endoscopic ultrasonography (EUS) is important in mediastinal staging of non-small cell lung cancer (NSCLC). Training standards and implementation strategies of this technique are currently under discussion. The aim of this study was to explore the reliability and validity of a newly developed EUS Assessment Tool (EUSAT) designed to measure competence in EUS - FNA for mediastinal staging of NSCLC.