The authors carried out genetic analyses and visual electrophysiologic evaluations in six asymptomatic sons and daughters of patients with symptomatic cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Three subjects showed Notch3 Cys146Tyr missense mutation and a dysfunction of the outer, middle, and innermost retinal layers, with normal neural conduction in postretinal visual pathways, whereas in the remaining subjects without genetic mutations, no electrophysiologic abnormalities were found. An early vascular retinal impairment in CADASIL may precede the onset of clinical manifestations.