ObjectiveTo elucidate sex differences in valve morphology, disease phenotype, progression, and outcomes among children and young adults with bicuspid aortic valve (BAV). Patients and MethodsThis is a retrospective cohort study examining all children and young adults (aged ≤22 years) with isolated BAV diagnosed, by excluding patients with concomitant congenital heart defects or genetic syndromes, from January 1, 1990, through December 1, 2016, at Mayo Clinic in Rochester, Minnesota. ResultsOf 1010 patients with BAV, 558 had isolated BAV. Distributions of morphology were right-left in 65.8% (n=367), right-noncoronary in 34% (n=190), and left-noncoronary cusp fusion in 0.2% (n=1) of patients; with no sex differences. Male to female ratio was 3:1. At the first echocardiographic evaluation in the study, there were no sex differences in terms of frequency of aortic valve stenosis or regurgitation. However, males had significantly higher grades of aortic valve regurgitation at 17 years of age onward (P<.0001). Males had significantly larger mid-ascending aorta (P=.01) and sinus of Valsalva dimensions (z score; P=.0001) as compared with females, with a novel finding of peak aortic dimensions around 8 years of age. Males also had more than 2-fold higher risk for sinus of Valsalva dilation (z score >2) as compared with females (odds ratio, 2.3; 95% CI, 1.2 to 4.2; P=.01). There were no significant sex differences in the primary cardiac outcomes of interventions on aortic valve and/or aorta, aortic dissection, or death. ConclusionIn children and young adults with BAV, males have a higher grade of aortic regurgitation in late adolescence, significantly larger aortic dimensions, different patterns of aortic growth, and more frequent sinus of Valsalva dilation as compared with females. Overall, the rate of primary cardiac events is lower in young patients, with no significant sex differences.