The detachable coils have been successfully used for transcatheter occlusion of small- to moderate-sized patent ductus arteriosus (PDA). We report our experience regarding the use of the Nit-Occlud coils (NOCs) for transcatheter PDA and major aortopulmonary collateral (MAPCA) occlusion. Single NOCs were used to close PDA in 26 patients, and one small and two large MAPCAs in two patients. Mean age and weight of the patients were 7.7 +/- 5.4 years and 20.6 +/- 11.6 kg. Mean minimum duct diameter was 2.8 +/- 0.8 mm; ampulla, 8.7 +/- 2.4 mm; and PDA length, 9.3 +/- 4.4 mm. Mean pulmonary artery pressure ranged from 9 to 51 mm Hg and pulmonary/systemic flow ratio from 1.1 to 5.8. Ductal shape was conical in 24 patients. Route of approach was venous in 23 and arterial in 3. Successful coil implantation was achieved in 24/26 (92.3%). Mean procedure and fluoroscopy time were 67.2 +/- 22.1 and 14.9 +/- 6.5 min. The three MAPCAs were also successfully occluded using NOC Medium and Flex. Postimplantation angiograms revealed no leak in 3, a trace or small leak in 17, and a medium leak in 4 patients. Mean follow-up was 7 +/- 5 months. Complete occlusion was achieved in 17/24 (71%) at 24 hr, 19/24 (79%) by 1 month, 13/15 (87%) by 3 months, 14/15 (93%) by 6 months, and 10/11 (90%) by 12 months postprocedure. Hemolysis, late embolization, duct recanalization, and flow disturbances were not observed. Transcatheter occlusion of moderate-sized PDAs and MAPCAs using NOCs seems to offer a safe, simple, and controlled method in pediatric patients.