Abstract Funding Acknowledgements Type of funding sources: None. Background Previous studies have reported major sex differences in prevalence, demographics, and timing of intervention in left ventricular outflow tract (LVOT) obstruction. Whether the observed differences are related to LVOT anatomy is less explored. Purpose The aim of this study was to assess the anatomic substrate for LVOT obstruction by echocardiography to identify sex-specific phenotypes. Methods We included 76 patients (37% women) with symptomatic LVOT obstruction referred to a tertiary care centre between 2005-2020 to be considered for septal ablation or myectomy. A standardized echocardiography was extended with systematic measurements of parasternal LVOT dimensions at 5, 10 and 15 mm below the aortic valve, proximal septal thickness at 10, 20 and 30 mm, subaortic septal bulge radius and aortoseptal angle in all patients prior to intervention (Image). Measurements were also adjusted for body surface area (BSA). A total of 3 patients had to be excluded from analysis due to poor image quality. Results Women were older (p < 0.001, Table), while there were no differences in body mass index (27.6 v.s. 27.5, p = ns), systolic and diastolic blood pressure (133 v.s 133 mmHg, p = ns and 75 v.s 80 mmHg, p = ns, respectively), or prevalence of hypertension (24% v.s. 29%, p = n.s). Left ventricular end-diastolic diameter, LVOT diameters and septum thickness measured 30 mm from the aortic valve were lower in women (Table). However, in all these measurements the differences disappeared after adjusting for BSA. There were no sex differences in posterior wall thickness. Furthermore, the aortoseptal angle was steeper among women, and the septum bulge radius smaller, remaining so even after adjustment for BSA(Table). Conclusion In women with LVOT obstruction, the septum bulge radius adjusted for BSA was smaller, and the aortoseptal angle steeper. Our findings suggest that there may be important sex differences in the echocardiographic phenotype in LVOT obstruction. Abstract Table Abstract Figure. Image