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. Chin Med J 2012;125(19):3388-3392