The aim of this study was to evaluate whether left ventricular (LV) systolic strain in children and young adults with congenital aortic stenosis (AS) and preserved ejection fraction was different from normal subjects and to determine whether any alterations in strain were related to myocardial fibrosis. In this retrospective study, 29 patients with congenital AS with a median age of 15.3 years (range 1.7 to 23.7), highest lifetime AS peak Doppler gradient of 73 mm Hg (22 to 110), most recent AS peak Doppler gradient of 49 mm Hg (0 to 90), and ejection fraction of 65 (55 to 79) were included. Strain was measured using 2-dimensional speckle-tracking echocardiography. Cardiac magnetic resonance was used to identify focal fibrosis by late gadolinium enhancement (LGE) and diffuse fibrosis by calculating the extracellular volume fraction (ECV) from T1 measurements. Compared to age-matched controls (n = 29), patients with AS had reduced LV longitudinal (17.0 ± 3.0% vs 20.6 ± 2.2%, p <0.001) and radial strain (28.8 ± 8.6% vs 34.9 ± 8.5%, p = 0.01), and similar circumferential strain (26.2 ± 5.9% vs 26.4 ± 3.9%, p = 0.79). Median ECV in patients with AS was 0.27 (0.22 to 0.38) and was not significantly correlated with systolic strain. Patients with LGE (n = 7) had lower longitudinal strain than those without LGE (n = 21; 15.0 ± 2.2 vs 17.7 ± 3.1, p = 0.036). In conclusion, in this cohort of children and young adults with congenital AS and preserved ejection fraction, longitudinal and radial strain were reduced, and decreased longitudinal strain was associated with LGE but not ECV.