We investigated whether carotid sinus hypersensitivity (CSH) and orthostatic hypotension (OH) were associated with a greater severity of hyperintensities on MRI scan in 30 patients with neurodegenerative dementia (17 dementia with Lewy bodies, 13 Alzheimer's disease), who had a detailed evaluation of OH and CSH during active standing and head-up tilt. Patients also underwent a 1.0 Tesla MRI scan, from which hyperintensities were rated on a standardized scale. A blood pressure (BP) drop > 30 mm Hg during carotid sinus massage or active standing was significantly associated with the severity of MRI hyperintensities in the deep white matter (OR 10.0, 95%; CI 1.8-55.7) and in the basal ganglia (OR 11.0, 95%; CI 1.2-99.5) but not in periventricular areas (OR 1.4, 95%; CI 0.3-1.8). Patients with the cardio-inhibitory form of CSH with the largest BP drops were the most at risk. Further longitudinal studies need to investigate the direction of causality to determine whether CSH or OH predispose to MRI hyperintensities and accelerate cognitive decline.