Context: Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy and cause of cardiac transplantation in children. However, the epidemiology and clinical course of DCM in children are not well established. Objective: To provide a detailed description of the incidence, causes, outcomes, and related risk factors for DCM in children. Design and Setting: Longitudinal study based on a population-based, prospective cohort of children diagnosed as having DCM since January 1, 1996, at 89 pediatric cardiac centers and a retrospectively collected cohort of patients seen primarily at large tertiary care centers in North America and who had diagnoses between January 1, 1990, and December 31, 1995, and were enrolled through February 2003. Participants: A total of 1426 children from the United States and Canada diagnosed as having DCM at younger than 18 years. Primary DCM was determined by strict echocardiographic and/or pathologic criteria. Patients with disease due to endocrine, immunologic, drug toxicity, and other causes were excluded. Main Outcome Measures: Annual incidence per 100 000 children; mortality; cardiac transplantation. Results: The annual incidence of DCM in children younger than 18 years was 0.57 cases per 100 000 per year overall. The annual incidence was higher in boys than in girls (0.66 vs 0.47 cases per 100 000; P<.001), in blacks than in whites (0.98 vs 0.46 cases per 100 000; P<.001), and in infants (<1 year) than in children (4.40 vs 0.34 cases per 100 000; P<.001). The majority of children (66%) had idiopathic disease. The most common known causes were myocarditis (46%) and neuromuscular disease (26%). The 1- and 5-year rates of death or transplantation were 31% and 46%, respectively. Independent risk factors at DCM diagnosis for subsequent death or transplantation were older age, congestive heart failure, lower left ventricular fractional shortening Z score, and cause of DCM (P<.001 for all). Conclusions: In children, DCM is a diverse disorder with outcomes that depend largely on cause, age, and heart failure status at presentation. Race, sex, and age affect the incidence of disease. Most children do not have a known cause of DCM, which limits the potential for disease-specific therapies.