INCLUSION CRITERIA:  Eligibility for this study may be determined based on information collected under other NHLBIapproved protocols, outside records and patient report. In order to be eligible to participate in this study, an individual must meet criteria 1 & 2 and either criteria 3 or 4:  Stated willingness to comply with all study procedures and availability for the duration of the study. Male or female, aged 18 to 100 years (inclusive). Established diagnosis of CADASIL, as determined by genetic testing. Healthy controls.  EXCLUSION CRITERIA:  An individual who meets any of the following criteria will be excluded from participation in this study:  Pregnancy or nursing at time of consent. Subjects who lack capacity to consent and don't have a legally authorized representative. Subjects who decline to provide samples for blood and/or tissue studies. Subjects who do not speak English. Subjects whose scans or examinations show unexpected brain conditions (outside of CADASIL) which would interfere with interpretation of testing.  Subjects unable to undergo an MRI scan or subjects meeting the following criteria:  Subjects who have internal non-MRI compatible metals (i.e. cardiac pacemaker, brain stimulator, shrapnel, surgical metal, clips in the brain or on blood vessels, cochlear implants, artificial heart valves or metal fragments in the eye) as these rendering an MRI unsafe Subjects with ferromagnetic dental bridges or crowns (exclusion only for 7.0T) Subjects unable to remain supine for the expected length of the MRI (i.e. up to 1 hour) Subjects with uncontrolled head movements Subjects who are claustrophobic for the expected length of the MRI (i.e. up to 1 hour) and claustrophobia cannot be controlled with anti-anxiety medication.