Data from studies of dementia prevalence between 1945 to 1985 were analyzed statistically. Prevalence rates were found to vary as a function of methodological differences between studies. However, despite these differences, the relationship between prevalence and age was found to be consistent across studies, with rates doubling every 5.1 years. Across studies, Alzheimer's disease (AD) was found to be more common in women, with a tendency for multi-infarct dementia (MID) to be more common in men. There were also national differences in the relative prevalence of AD and MID, with MID being more common in Japanese and Russian studies, no difference in Finnish and American studies, and an excess of AD in other Western European countries.