To evaluate the feasibility of transcatheter closure of secundum atrial septal defects (ASDs) associated with deficient rims (<5 mm) using the Amplatzer septal occluder (ASO), 23 patients (median age 10.7 years) underwent an attempted transcatheter closure. The patients had a deficient anterior rim of 0 to 4 mm (n = 20), an inferior rim of 2 mm (n = 2), or a posterior rim of 4 mm (n = 1) as assessed by transesophageal echocardiography (TEE) or intracardiac echocardiography (ICE). Forty-eight patients with sufficient rims (>5 mm) who underwent closure served as controls. There were no differences between the 2 groups in ASD stretched diameter and device size (p >0.05). Of 23 patients with deficient rims, 17 (74%) had immediate complete closure compared with 44 of 48 patients (92%) with sufficient rims (p <0.05). At 24-hour and 6-month follow-up, the complete closure rates were not significantly different between the 2 groups (91% for patients with deficient rims vs 94% for patients with sufficient rims at 24 hours and 100% vs 93% at 6 months, respectively). The fluoroscopic time and procedure time were longer in patients with deficient rims (13 +/- 7 and 72 +/- 26 minutes, respectively) compared with those with sufficient rims (10 +/- 4 and 61 +/- 22 minutes, respectively). No major complications were encountered either during or after the closure procedure in both groups. Thus, transcatheter closure of ASDs associated with small anterior, inferior, or posterior rims is feasible using an ASO. Long-term follow-up data are still needed to assess long-term safety and efficacy.