The outcome of medical treatment of dilated cardiomyopathy in infants and children was reviewed to develop a predictive index for selection of patients likely to benefit from cardiac transplantation. The clinical findings, laboratory investigations, treatment and outcome of 20 patients (Group 1) less than 2 years of age at presentation and 12 patients (Group 2) greater than 2 years of age at onset were compared. Of 20 Group 1 patients, 5 (25%) died. Available autopsies (four patients) showed endocardial fibroelastosis. Of 15 survivors, 10 showed improvement in cardiac status and 5 remained unchanged. Ninety-three percent of survivors had dilated cardiomyopathy consistent with endocardial fibroelastosis by angiocardiography. All 12 Group 2 patients died. In addition to age at presentation and poor outcome, Group 2 differed from Group 1 in having a higher incidence of other family members with cardiomyopathy, more significant rhythm disturbances at presentation and a more rapid course to death. Risk factors of poor outcome in both groups included persistent cardiomegaly and the development of significant arrhythmias by Holter electrocardiographic monitoring. Cardiac transplantation is recommended for children with dilated cardiomyopathy presenting after age 2 years who survive 1 month. Those patients less than 2 years old at presentation whose condition has not improved after 1 year and who have persistent cardiomegaly or complex ventricular arrhythmias may also benefit from transplantation.