We report a unique longitudinal epidemiological study of cognitive decline in the elderly population of the city of Cambridge, UK. A population sample of people aged 75 and over was surveyed between 1984-1996 (n = 2,616) and followed 2.4, 6, and 9 years later. CAMDEX diagnostic criteria were used for clinical assessment, and the neuropathological protocol (in 101 cases) was based on the CERAD method, with additional features to allow Braak staging of neurofibrillary pathology. The main findings are of the heterogeneity of lesions to be found in very old populations, and the existence of considerable overlap in the pathologies found in the demented and nondemented. It seems that white matter (ischemic) pallor an amyloid angiopathy, as well as neuritic plaques, neurofibrillary tangles and Lewy body formation are all lesions that increase the likelihood of dementia.