AIMS The aim of this study was to analyse the relation between endothelial dysfunction (ED) and the occurrence of radial artery spasm (RAS) during transradial coronary procedures. METHODS AND RESULTS From May 2014 to June 2015, endothelial function was assessed by EndoPAT and FMD before the procedure in 165 patients referred for coronary angiography or intervention. The primary endpoint was RAS, defined by patient's symptoms and procedural characteristics. The mean age of the study population was 63 years and 71% were male. In total 16% of the patients experienced RAS. The incidence of RAS did not differ between patients with and without ED (13.8% vs. 20.2%, OR 0.63, 95% CI: 0.25-1.58, p=0.32). The strongest predictors of RAS were a ratio of radial artery inner diameter and sheath outer diameter smaller than 1 (OR 4.7, 95% CI: 1.35-16.5, p=0.009) and a combination of clinical characteristics presented as an RAS risk score of at least 4 (p=0.007, OR 3.7, 95% CI: 1.37-9.89). CONCLUSIONS Endothelial dysfunction was not found to be a predictor of the occurrence of radial artery spasm in a cohort of patients undergoing elective heart catheterisation. Radial artery-sheath mismatch is the strongest pre-procedural predictor of RAS.