The objective of this study was to describe a new technique for transcatheter device closure of large atrial septal defects (ASDs) using the Amplatzer septal occluder and our experience with this technique in 14 patients. Transcatheter closure of large (> 25 mm) ASDs is challenging. We have developed a balloon-assisted technique (BAT) to facilitate device closure of large ASDs. The BAT consists of using a balloon catheter to support the left atrial (LA) disk of the Amplatzer septal occluder during device deployment. The balloon support prevents prolapse of the LA disk into the right atrium. Between April 2003 and February 2004, 14 patients with large ASDs (mean age, 25.71 +/- 15.71 years; mean weight, 51.21 +/- 23.78 kg) underwent device closure with the Amplatzer septal occluder using the BAT. The median balloon-stretched diameter of the ASD was 32 (range, 26-40) mm. The median device size used was 33 mm (range, 26-40 mm). All 14 patients had successful deployment of the device using the BAT. The mean follow-up period was 16.5 +/- 11.95 weeks. No major complications were noted during the procedure or on short-term follow-up. The BAT enables predictably successful closure of large ASDs using the Amplatzer septal occluder.