BACKGROUND: Coronary chronic total occlusion(CTO) are commonly encountered complex lesions. Despite improving techniques for opening CTO, the benefit of successful recanalization remains unclear. Transradial coronary intervention (TRI) is a safe and effective method of percutaneous coronary intervention (PCI). However, there is limited data on the efficacy of TRI for CTO. To investigate the efficacy and safety of TR PCI for CTO, and to compare the outcome of successful versus failed procedures. METHODS: 176 consecutive CTO patients, who underwent PCI due to typical angina between June 2006 and February 2009 were analyzed. According to vascular access site, we divided into 2 groups: Group I (TRI, n=72, 63짹10 yrs) and Group II (TFI, n=104, 67짹9 yrs). We compared baseline and angiographic characiteristics, procedural success rate, and major adverse cardiac event (MACE; cardiac death, MI, TVR) at 1-, 6- and 12-month. RESULTS: There were no differences in clinical characteristics such as diabetes (39 vs. 33%) between the two groups. In angiographic findings, rate of multi-vessel disease (81 vs. 86%, p=0.7), blunt stump (58 vs. 39%, p=0.1), heavy calcification (26 vs. 17%, p=0.3), and dissection were not different between groups. Furthermore, procedural success rate (78.4 vs. 70.8%, p=0.5), MACE at 1 month (4.4 vs. 5.6%, p=0.8), 6 months (14.0% vs. 22.2%, p=0.4), and 12 months were not significant different between the two groups. Coronary perforation during the initial failed attempts occurred in 4.1% of patients (2 of 48). After an average follow-up period of 1 year, patients with successful or failed procedures experienced no difference in MACE (23.2% and 26.7%, respectively, p =0.473). CONCLUSION: TRI may be not inferior than TFI in procedural success and long-term clinical outcome. But, there was no difference in clinical outcomes between successful and failed procedures group. Further large trial should be need.