Few European families have been reported with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). We describe four patients from two independent American families. All four cases underwent comprehensive clinical, neuropsychological and pathological examination. Pathological data were correlated with clinical features. Dementia was a prominent and constant feature in all subjects. The families differed in phenotypical presentation and we analyzed possible pathological substrates that may account for the differences. Autopsy showed multiple ischemic infarcts in the white matter, abnormal vasculature with thickening and degeneration of the vessel wall. The clinical course in the first family was characterized by early dementia without stroke-like episodes; however, autopsy demonstrated strokes in the basal ganglia and thalamus. The members of the second family developed dementia later and had history of several clinically evident strokes. Pathological examination showed only widespread degeneration of the white matter. Our study of two American families with CADASIL suggests that involvement of the basal ganglia and thalamus is important for early development of dementia and clinically can present as a gradual dementia, resembling a neurodegenerative process. Selective damage of the white matter and central gray matter provides further insight to the pathogenesis of vascular dementia.