Abstract    BACKGROUND: Chronic total occlusion of coronary arteries (CTO) remains one of the most challenging lesion subsets in interventional cardiology even with the development of medical devices and operator expertise. This study sought to determine the overall success rate of percutaneous coronary intervention (PCI) for this lesion in the center and to examine the relationship between variables such as patients’ characteristics, clinical risk factors, lesion characteristics and procedural success rate.    METHODS: Clinical and coronary angiographic data of 58 patients with CTO who underwent PCI between May 2004 and November 2006 in Ghaem Hospital were retrospectively analyzed. A P value of less than 0.05 was considered statistically significant. Analyses were performed using the software packages SPSS (11.5 version).    RESULTS: In this study, there were 58 CTO lesions in 41 men (70.7%) and 17 women (29.3%) with a mean occlusion time of 5 months. The overall success rate of PCI was 77.6%. There was no significant correlation between the success rate of PCI and the patient’s age, sex, clinical risk factors, history of recent MI and duration of occlusion (P > 0.05). The success rate was not affected by target vessel, location of lesion, presence of stump, presence of side branch at the site of occlusion and TIMI flow of artery (P > 0.05). The success rate of PCI was decreased with increase in the length of occlusion and presence of bridging collaterals (P < 0.05).     CONCLUSION: The length of occlusion and presence of bridging collaterals affected the success rate adversely. Whereas the patients’ characteristics, clinical risk factors and other characteristics of coronary artery lesion had no statistically significant effect on success rate of PCI. Despite the technical difficulty of PCI in CTO lesions, this procedure can be done safely with relatively high success rate.      Keywords: Chronic total occlusion (CTO), percutaneous coronary intervention (PCI), coronary arteries.