Patients with childhood heart disease are living longer and entering adulthood, and may undergo implantable cardioverter-defibrillator (ICD) implantation to reduce the risk of sudden death. We evaluated the characteristics of adult patients with congenital heart disease or left ventricular noncompaction cardiomyopathy (LVNC) in the National Cardiovascular Disease Registry ICD Registry and determined ICD-related in-hospital complications. Patients with LVNC or transposition of the great arteries, tetralogy of Fallot, Ebstein's anomaly, atrial septal defect, ventricular septal defect, or common ventricle were identified in the registry. In-hospital complications were compared among different diagnoses using the chi-square test for categorical variables and the F-test in analyses of variance for continuous variables. A total of 3,077 patients were identified. The mean age was 48.0 ± 16.0 years, and 39.9% were female. Single-chamber ICDs were implanted in 25.2%, dual chamber in 41.9%, and cardiac resynchronization in 30.8%. Intraprocedural or postprocedural complications occurred in 70 patients (2.3%); there were 6 in-hospital deaths (0.2%). The most frequent complications were acute lead dislodgments, pneumothorax, and hematomas. Patients with Ebstein's anomaly had the greatest complication rate (8.3%, p = 0.03). The complication rate was 1.55% in single-chamber devices, 1.86% in dual chamber, and 3.5% in cardiac resynchronization (p < 0.001). For initial implants, the complication rate was 2.55%, 1.62% in generator replacements, and 8.77% in lead revisions (p = 0.001). In conclusion, in this large contemporary adult cohort of congenital heart disease and LVNC patients who underwent ICD implant procedures, periprocedural complication rates were low. Lead-related risks predominated.