Intracardiac thrombosis in patients with a dilated cardiomyopathy can be life threatening. This study investigated the incidence, risk factors, and outcome of intracardiac thrombosis in children with dilated cardiomyopathy. A retrospective review of the clinical records was performed in 83 children with dilated cardiomyopathy diagnosed from January 1995 to December 2008. Intracardiac thrombi were detected in 5 patients (6.0%). The intracardiac thrombi were found mainly in the left ventricle (n = 3). One patient had a thrombus in the left atrium at the time of diagnosis, and a right ventricular thrombus was found in 1 patient with unrepaired ventricular septal defect complicated by pulmonary hypertension. Intracardiac thrombosis developed during rapid deterioration of ventricular function, and all patients had a poor ejection fraction of the left ventricle. All patients were treated with heparinization, and thrombectomy was performed in 1 patient. Three patients achieved complete resolution of the thrombus without further embolic complications. Careful evaluation and aggressive anticoagulation are necessary for the prevention of intracardiac thrombosis in children with poor ventricular function, especially during rapid deterioration of ventricular function.