From 1968 through 1973, 1,915 deaths in the United States were attributed to senile dementia, and 1,463 deaths were attributed to presenile dementia. The corresponding average annual age-adjusted mortality rates per million population (adjusted to the 1970 US population) were 5.2 and 3.9, respectively, suggesting considerable underreporting. In view of the limitations associated with the analysis of causes of death, these data should be interpreted with caution. The average annual age-specific mortality rates for all dementias combined display a smooth, continuously rising curve with increasing age. This finding is consistent with the hypothesis that the majority of deaths attributed to presenile dementia and the majority of deaths from senile dementia are the result of the same disease entity.