We evaluated the circadian changes of blood pressure in the elderly with Alzheimer's type dementia with ambulatory blood pressure monitoring (ABPM-630, Nihon Colin, Aichi, Japan). Blood pressure and heart rate were high in the daytime and low in the nighttime in the elderly without dementia. Blood pressure did not decrease in the nighttime in the elderly with dementia, although heart rate decreased. Thus, the circadian rhythm of blood pressure was selectively impaired in the elderly with Alzheimer's type dementia.