The symptoms of Alzheimer's disease are associated with pathological change and loss of neurons in the medial temporal lobe. By yearly temporal-lobe-oriented computed tomograms the average rate of atrophy of the medial temporal lobe was 15.1% per year (95% CI 10.0, 20.2) in 20 patients with histopathologically, confirmed Alzheimer's disease and 1.5% (0.2, 2.8) in 47 healthy ageing controls. Such excessive atrophy presumably reflects the vulnerability of the medial temporal lobe to a catastrophic event, probably a pathological cascade process. Thus, Alzheimer's disease may not be due simply to an acceleration of normal ageing but, rather, is the consequence of a true disease process.