Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy in children, but its epidemiology and clinical course are not well established. Towbin and colleagues reviewed data from 2 cohorts of children with primary DCM to advance understanding of this disease. They found a higher risk in boys than in girls, in black than in white children, and in infants than in children. Two thirds of cases were idiopathic, but important identifiable causes were myocarditis and neuromuscular disease. Outcomes were influenced by age, heart failure status at diagnosis, and cause.