Background Obesity is highly prevalent in patients with hypertrophic cardiomyopathy (HCM) and believed to influence its phenotype. Purpose To explore the effects of obesity on left ventricular (LV) remodeling and long-term clinical course in Chinese patients with HCM. Study Type Longitudinal. Population A total of 247 patients with HCM classified according to body mass index (BMI) (normal weight: BMI = 18.0-22.9 kg/m(2) [N = 90]; overweight: BMI = 23.0-24.9 kg/m(2) [N = 58]; and obese: BMI >= 25 kg/m(2) [N = 99]). Field Strength/Sequence 3.0 T/Balanced steady-state free precession sequence and phase-sensitive inversion recovery late gadolinium enhancement (LGE) sequence. Assessment LV function and geometry were measured. LV peak strain analysis was performed. The presence and percentage of LGE in the LV were recorded. The endpoints including heart failure, sudden cardiac death, and overall composite outcome were assessed during a median follow-up of 4.1 years (interquartile range, 3.0-6.2 years). Statistical Tests One-way analysis of variance, Kruskal-Wallis test, or chi-square test; Pearson correlation coefficient (r); multivariable linear regression analysis; Kaplan-Meier survival analysis; and Cox proportional hazards model analysis were conducted. A two-tailed P-value < 0.05 was considered statistically significant. Results Obese patients exhibited a significant progressive increase in LV mass compared with normal-weight patients. The magnitude of all LV strain indices gradually and significantly decreased as BMI increased, whereas LV ejection fraction was not significantly different among BMI groups (P = 0.364). Multivariable linear regression analysis showed that obesity had a significant association with impaired strain indices as well as with indexed LV mass. Multivariable Cox model analysis retained obesity as an independent marker for future endpoints, and conveyed a > 3-fold increase in risk compared with patients with normal weight (hazard ratio, 3.04; 95% confidence interval, 1.07-6.57). Data Conclusion Obesity is an important environmental modifier that is associated with adverse LV remodeling and is independently associated with future clinical outcomes in Chinese patients with HCM. Level of Evidence 3 Technical Efficacy Stage 2