We present the clinical, imaging, and neuropathologic data for a family with an autosomal dominant, nonhypertensive, progressive cerebral arteriopathy and leukoencephalopathy. Clinical presentation was characterized by progressive dementia, gait abnormalities, and, in some, Parkinson-like symptoms. MR abnormalities, consisting of white matter T2 hyperintensities and cystic-appearing T1 hypointensities, were present in seven family members. The basal ganglia also showed cystic abnormalities. Neuropathologic examination in two cases revealed numerous lacunar infarctlike lesions, extensive demyelination, and widespread hyalinization of arteriolar walls with karyolysis and granular deposits within the media. These findings appear to constitute further evidence of a genetically determined arteriopathic leukoencephalopathy.