Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are two different diseases and have distinct etiologies. HCM is rare in children and rarely progresses to DCM. We report a 5-year-old Taiwanese girl with a definite diagnosis of hypertrophic obstructive cardiomyopathy. The diagnosis was based on echocardiograms, cardiac catheterization, and endomyocardial biopsy. However, the clinical features progressed to a picture of nonobstructive HCM at age 9, and the patient developed dilated poorly contractile ventricles with intractable congestive heart failure at age 10. She died from ventricular tachycardia at age 13. This report emphasizes the importance of periodic reevaluation for children with HCM.