Implantable cardioverter defibrillators (ICDs) are being used with increasing frequency in children and young adults. Our aim was to examine the appropriateness and frequency of ICD discharges in children and young adults, to compare the effectiveness of ICDs when placed for primary or secondary prevention, and to provide time-dependent analysis of ICD discharges. Data were collected from seven institutions on 210 patients <30 years of age who underwent ICD implantation from October 1992 to January 2007. Median age at implant was 15.4 years with a follow-up average of 3.3 years. Heart disease was categorized as electrical (n = 90, 42%), cardiomyopathic (n = 62, 30%), or congenital heart disease (n = 58, 28%). ICDs are increasingly placed for primary prevention. There are increased appropriate ICD discharges for ICDs placed for secondary prevention (52%) versus primary prevention (14%) at 5 years. There is no difference in the risk of inappropriate discharges between primary and secondary prevention indications. There is an increased risk for inappropriate therapy in the congenital heart disease population. An increasing number of ICDs are being placed for primary prevention in young patients, a marked shift in practice during the last two decades. The benefits of ICDs remain greater in secondary than in primary-prevention patients. In both groups, approximately 25% of patients received inappropriate discharges within 5 years of implant. Patients with congenital heart disease are the most affected by inappropriate discharges.