Background: Intracardiac echocardiography (ICE) was introduced as a new guidance system for transcatheter closure of secundum atrial septal defect (ASD) with Amplatzer septal occluder® (ASO). The aim of this study was to investigate the clinical outcome of ICE-guided transcatheter closure of ASD compared with the trans-esophageal echocardiography (TEE)-guided method. Methods and Results: From May 2003 to April 2010, 560 patients who underwent transcatheter closure of ASD using ASO in a single institute were analyzed retrospectively. In the TEE-guided group (n=237), all the patients underwent general anesthesia. The median age was 24.2 years (range, 14 months–63 years) and the average weight was 42.3±21.6kg (range, 8.2–82kg). One patient underwent surgery due to migration of device. The remaining 236 patients underwent the procedure successfully without significant complication. In the ICE-guided group (n=323), the median age was 30.5 years (range, 7 months–75 years). One patient underwent surgery because of mitral valve encroachment by left atrial disk after device placement. Another patient also underwent surgery due to device embolization. The remaining 321 procedures were performed successfully without major complications. Procedure time was 104.2min and 87.7min, respectively (PConclusions: ICE-guided ASD occlusion with ASO is safe and effective and provides accurate anatomical information, sufficient to perform the procedure. In addition, there were benefits of avoidance of general anesthesia, and shorter procedure time. (Circ J 2012; 76: 2119–2123)