To examine the neuropathological characteristics of senile dementia of the Alzheimer type (SDAT) in very old people, we performed a quantitative analysis of the distribution of neurofibrillary tangles and senile plaques in the brains of 12 demented patients aged from 96 of 104 years. The hippocampal formation and the inferior temporal cortex displayed numerous neurofibrillary tangles in most cases, whereas the superior frontal cortex was relatively spared. The only statistically significant difference between demented and control cases was in the density of neurofibrillary tangles in the CA1 field of the hippocampus. High senile plaque densities were observed in the cerebral cortex and were correlated with the duration of SDAT. These results confirm the crucial role of the hippocampus in the neuropathological diagnosis of SDAT in oldest-old patients. Furthermore, they suggest that senile plaque formation may be a pathological hallmark of severe SDAT in this particular age group.