Hypertrophic cardiomyopathy (HCM) is the most prevalent genetic cardiomyopathy in children and young adults. Despite advances in understanding the molecular etiology of this disorder, the clinical phenotypes vary widely from asymptomatic septal hypertrophy, to frank congestive heart failure due to left ventricular outflow tract obstruction (LVOTO), to unexpected sudden cardiac death. Thus, isolating a specific genetic defect in this disease does little to predict the clinical consequence. This is best seen in large families with several people affected by HCM who all have the identical mutation but who may have very different clinical phenotypes. Evaluating individuals with HCM consists of establishing the diagnosis through cardiac imaging, noninvasively assessing the risk for sudden death, and medically or surgically treating symptomatic LVOTO when it is present.