We report the early complications of stent implantation. Since 1/1/97 to 1/12/02, we implanted 91 stents in 76 patients. Median age and weight were 15 years (range 0.3-43) and 49 kg (range 3-96). Primary diagnosis were: pulmonary atresia with ventricular septal defect (n = 17), tetralogy of Fallot (n = 13), aortic coarctation (n = 15), transposition of the great arteries (n = 3), truncus arteriosus (n = 6), univentricular heart (n = 7), other anomalies (n = 28). Indications to stent implantation were: stenosis of the pulmonary outflow and/or pulmonary branches (n = 44), aortic recoarctation (n = 14), native aortic coarctation (n = 1), systemic venous channels obstruction (n = 14), other (n = 3). The stents were: Palmaz (n = 57), non premounted CP (n = 8), premounted CP (n = 3), Palmaz Corinthian (n = 19), self-expanding (n = 4). Procedural complications occurred in 24 patients (31%) and included: 11 balloon bursting, 8 stent slipping, 1 stent migration, 4 wall dissections. Five patients (21%) needed urgent surgery. Sixty three percent of complications occurred during pulmonary outflow or pulmonary branches stenting, 25% during stenting of the aortic arch, 12% during other procedures. All but 2 complications were observed with non premounted stents. In conclusion, the use of not premounted stents, although widely diffuse, has a not negligible incidence of complications, leading to longer procedures, to the use of a large variety of materials and needing more than occasionally a surgical solution. A larger use of premounted stents, when possible, is recommended.