Abstract Objectives We sought to assess the long-term outcomes in patients with hypertrophic cardiomyopathy and severe left ventricular outflow tract obstruction, in whom the decision regarding surgery (vs conservative management) was based on assessment of symptoms or exercise capacity. Methods This was an observational study of 1530 patients with hypertrophic cardiomyopathy (aged 50 ± 13 years, 63% were men) with severe left ventricular outflow tract obstruction (excluding those aged <18 years, with left ventricular ejection fraction <50%, and with left ventricular outflow tract gradient <30 mm Hg). A composite end point of death (excluding noncardiac causes) and/or implantable defibrillator discharge was assessed. Results Coronary artery disease, family history of hypertrophic cardiomyopathy, and syncope were present in 15%, 17%, and 18% of patients, respectively, whereas 73% patients were in New York Heart Association class II or greater. Mean left ventricular ejection fraction, basal septal thickness, and left ventricular outflow tract gradient (resting or provocable) were 62% ± 5%, 2.2 ± 1 cm, and 101 ± 39 mm Hg, respectively. A total of 858 patients (56%) underwent exercise echocardiography, of whom 503 (59%) had exercise capacity impairment. At 8.1 ± 6 years, 990 patients (65%) underwent surgical relief of left ventricular outflow tract obstruction, and 540 patients (35%) did not. There were 156 events (10%) (134 deaths), with 0% 30-day mortality in the surgical group. On multivariable Cox proportional hazard analysis, increasing age (hazard ratio HR, 1.20), coronary artery disease (HR, 1.68), worse New York Heart Association class (HR, 1.46), and atrial fibrillation (HR, 1.90) predicted higher events, whereas surgery (time-dependent covariate HR, 0.57) was associated with improved event-free survival (all P  < .01). Conclusions In patients with hypertrophic cardiomyopathy and severe left ventricular outflow tract obstruction, in whom the decision regarding surgery was based on the presence of intractable symptoms and impaired exercise capacity, surgery was associated with significant improvement in long-term composite outcomes.