The search for biologic markers of Alzheimer disease (AD) progression has thus far had limited success. A technique is described, involving magnetic resonance imaging, that can be used to follow the progress of brain atrophy and hence the loss of neuronal tissue. It involves acquisition of three-dimensional images of the brain on two consecutive occasions and their precise co-registration so as to assess the loss of tissue volume over time. Median loss of brain volume in a group of individuals with sporadic and familial AD ranged from about 5-20 ml/year compared to less than 2 ml/year for controls. Loss of cerebral tissue volume was also seen in two individuals from a pedigree with familial AD at a time when symptoms were only just apparent.