The extent of regional atrophy in ten patients, aged 52-74 years, dying with Alzheimer's disease uncomplicated pathologically by the effects of advanced old age or cerebrovascular disease, was quantified by image analysis of fixed coronal brain slices. Atrophy of the cerebral cortex was globally distributed, although the temporal lobe was most severely affected. Grey and white matter was in general affected equally. Atrophy was also present within the basal ganglia, particularly the caudate nucleus and putamen. Cerebral cortical atrophy is probably due mostly to neurofibrillary degeneration and loss of intrinsic pyramidal cells and their processes (grey matter) and axons (white matter) although loss of ascending subcortical fibres from regions such as nucleus basalis and locus caeruleus will contribute. Atrophy of the basal ganglia may relate to loss of descending cortical projections.