Background Transradial coronary intervention (TRI) introduces injury to the radial artery (RA) which will affect repeat transradial coronary procedure and the quality as a bypass conduit.We sought to compare the early radial injury after TRI between first-TRI and repeat-TRI by ultrasound biomicroscopy (UBM).Methods A total of 1116 patients who underwent the transradial coronary procedures were enrolled.The patients depending on whether for the first time to accept transradial coronary procedure were divided into first-TRI group and repeat-TRI group.The RA was examined by UBM before and one day after the procedure.Results Compared with first-TRI group,the mean RA diameter of repeat-TRI one day after the procedure decreased significantly (P ＜0.05).In first-TRI group,the mean RA diameter was (2.32±0.53) and (1.93±0.57) mm before procedure and one day after the procedure respectively (P ＜0.05).In repeat-TRI group,the mean RA diameter was (2.37±0.51) and (1.79±0.54) mm before procedure and one day after the procedure,respectively (P ＜0.01).Compared with first-TRI group,the mean RA diameter was reduced significantly in repeat-TRI group one day after the procedure (P＜0.05).The early radial injuries and intimal thickening were compared between first-TRI and repeat-TRI.The mean intima-media thickness of RA was (0.24±0.13) mm and (0.59±0.28) mm before procedure and one day after the procedure in first-TRI group.The mean intima-media thickness of RA was (0.29±0.16) mm and (0.68±0.32) mm before procedure and one day after the procedure in repeat-TRI group.Compared with first-TRI group,the mean intimal thickening was increased significantly in repeat-TRI group one day after the procedure (P＜0.05).Intimal dissection,stenosis and occlusion were all significantly greater in repeat-TRI RAs (P ＜0.05).Linear regression analysis revealed that diameter,repeated TRI procedure and PCI procedure were the independent predictors of intimal thickening.Conclusions RA early injuries were greater in repeat-TRI patients than in first-TRI patients.We first use high-resolution UBM imaging to demonstrate the rate of radial injury and revealed that diameter,repeated TRI procedure and PCI procedure were the independent predictors of intimal thickening.