Background Radiation skin injuries have been reported as a result of various procedures, so in the present study the patients' entrance skin dose (ESD) during percutaneous coronary intervention (PCI) was evaluated. Methods and Results ESDs were assessed during 97 procedures (13 for chronic total occlusion (CTO), 14 for multivessel stenoses, 22 for single-vessel multiple stenoses, and 48 for single stenosis). The patients wore jackets that had 48 or 52 radiosensitive indicators placed on the back during the PCI procedures, with 8 other indicators placed on both upper arms. After the procedure, the color of the indicators was analyzed with a color measuring instrument, and the patients' ESDs were calculated from the color difference of the indicators. The average maximum ESDs of the patients were 4.5±2.8 Gy (median: 4.6 Gy) for CTO, 2.3±0.7 Gy (median: 2.4 Gy) for multivessel stenoses, 1.8±1.0 Gy (median: 1.5 Gy) for single-vessel multiple stenoses, and 1.4±0.9 Gy (median: 1.2 Gy) for single stenosis. Conclusions Skin injury can occur during PCI, especially for CTO, so it is important to estimate each patient's ESD and attempt to reduce it. (Circ J 2006; 70: 44 - 48)