Hypertrophic cardiomyopathy (HCM) in infants and children is in many ways a distinct diagnosis from that seen in adults. The etiology, presentation, evaluation, treatment, and prognosis should all be considered as separate subjects when discussing pediatric versus adult patients. Although data from the adult literature in hypertrophic cardiomyopathy can be helpful and sometimes extrapolated to pediatric patients, data and outcomes from pediatric registries and studies are essential to a true understanding of hypertrophic cardiomyopathy in infants and children. In this chapter, we discuss the etiology and diagnosis of HCM in pediatric patients. Unlike the etiology of HCM in adults, children have a significantly more diverse range of causes, and the identification of the cause is essential to survival. There are over two dozen metabolic disorders and syndromes that can cause a phenotype of hypertrophic cardiomyopathy. Thus, genetic screening is helpful in pediatric patients and is more cost-effective. Clinical evaluation is significantly tailored to pediatric patients as the numerical data obtained during echocardiographic evaluation must be analyzed in relation to body surface area. Management of HCM in pediatric patients is not identical to management in adult patients; it carries different risks as it pertains to medication, surgery, and ICD placement. Lifestyle issues can be challenging as sports, exercise, and play are critical in a child’s physical, social, and emotional development. Appropriate risk stratification through additional cardiac testing such as Holter monitors and exercise stress testing is essential. These vital topics as well as treatment and prognosis are presented in detail in the following pages.