Elastin is a major component of conduit arteries and a key determinant of vascular viscoelastic properties. Aberrant organization of elastic lamellae has been reported in resistance vessels from spontaneously hypertensive rats (SHR) before the development of hypertension. Hence, we have characterized the content and organization of elastic lamellae in conduit vessels of neonatal SHR in detail, comparing the carotid arteries from 1-wk-old SHR with those from Wistar-Kyoto (WKY) and Sprague Dawley (SD) rats. The general structure and mechanics were studied by pressure myography, and the internal elastic lamina organization was determined by confocal microscopy. Cyanide bromide-insoluble elastin scaffolds were also prepared from 1-mo-old SHR and WKY aortas to assess their weight, amino acid composition, three-dimensional lamellar organization, and mechanical characteristics. Carotid arteries from 1-wk-old SHR exhibited narrower lumen and greater intrinsic stiffness than those from their WKY and SD counterparts. These aberrations were associated with heightened elastin content and with a striking reduction in the size of the fenestrae present in the elastic lamellae. The elastin scaffolds isolated from SHR aortas also exhibited increased relative weight and stiffness, as well as the presence of peculiar trabeculae inside the fenestra that reduced their size. We suggest that the excessive and aberrant elastin deposited in SHR vessels during perinatal development alters their mechanical properties. Such abnormalities are likely to compromise vessel expansion during a critical period of growth and, at later stages, they could compromise hemodynamic function and participate in the development of systemic hypertension.