The various structural components of the cortical degeneration of Alzheimer's disease were defined and graded. The severity of the degenerative process was thus mapped in different cortical areas where neuronal numbers and cortical width were also measured and compared with controls. Contrary to the general opinion that the degenerative process is rather uniformly diffuse, though accentuated in the medial temporal and frontal cortex, we found a consistent and more elaborate pattern with clearcut regional differences. Thus the degeneration involved, besides basal medial temporal limbic areas, the posterior cingulate gyrus and superior parietal lobule particularly, with somewhat less marked changes in the inferior parietal lobule and inferior temporal gyri. The sensorimotor, calcarine and anterior cingulate areas of the cortex were notably spared until very late stages. This regionally variable severity of the degeneration was also paralleled by a regionally varying reduction in neuronal numbers and cortical width, and agrees with our previously published results of a regional pattern which closely correlates with clinical parameters, including symptom pattern and regional cerebral blood flow alterations.