Introduction: While obesity is associated with adverse outcomes among adults with hypertrophic cardiomyopathy (HCM), there has been little work to describe its impact on outcomes among children with HCM. Hypothesis: Obesity is associated with increased in-hospital morbidity in pediatric patients with HCM. Methods: In this cohort study, data from 52 children’s hospitals contained in the Pediatric Health Information System database from 2009 to 2019 were analyzed. Patients aged 2-18 years old with a primary diagnosis of HCM were included and assessed for obesity based on ICD-9/ICD-10 codes. Patients with a concomitant diagnosis of a congenital heart disease were excluded. Results: Out of a total of 2,667 children with HCM, the prevalence of obesity was 9.6%. Obese patients were more likely to be male, Black, Hispanic, older at age of initial hospitalization, and have a family history of sudden cardiac death (Table 1). After adjusting for age, sex, race, and ethnicity in multivariable analysis, obesity was independently associated with arrhythmia (OR 1.390 [1.029-1.879], P=0.032), heart failure (OR 1.809 [1.247-2.624, P=0.002), number of admissions (IRR 1.349 [1.158-1.573], P<0.001), and cumulative length of stay (IRR 1.276 [1.093-1.491], P=0.002). Obesity was not associated with mortality. Conclusions: In pediatric patients hospitalized with a diagnosis of HCM, obesity was more common in underrepresented minorities and associated with increased morbidity after accounting for other risk factors. Reducing the burden of obesity in this population with effective counseling and lifestyle interventions may play a role in preventing obesity-related adverse outcomes.