Frontotemporal dementia (FTD) is believed to be much less common than Alzheimer’s disease (AD), but data on prevalence and incidence of FTD are very sparse. The lack of data is in large part the result of the lack of methodology for diagnosing and enumerating cases of FTD. With an incidence rate of AD of approximately 1 case per 100 patients, 1, 2 or a prevalence of 6% or higher3 among individuals over age 70, traditional methods of case ascertainment yield stable and reliable estimates for AD. Because of challenges it presents in clinical diagnosis, incidence or prevalence of FTD could not be estimated by the traditional methods of case identification.

What we currently know about the descriptive epidemiology of FTD comes largely from autopsy series. Because the neuropathological diagnosis of FTD was in flux until very recently, there has been a wide divergence of estimates of the incidence of FTD. One major reason for this variation derived from confusion over the relationships between Pick body–positive dementia (ie,“true” Pick’s disease to North American neuropathologists, or Pick’s type A), 4 dementia with swollen chromatolytic neurons (Pick cell dementia, corticobasal degeneration, or Pick’s type B), and dementia lacking distinctive histology (nonspecific degeneration, or Pick’s type C). Pathologists sometimes included only one or two of these variants in their “Pick’s disease” category. In addition, clinical-pathological series could have selection biases that might exclude individuals with the FTD phenotype. Some series report very few FTD cases. 5 Knopman and colleagues6 reviewed the experience of a brain bank in Minneapolis–St. Paul, Minnesota. Although FTD was infrequent overall (approximately 6%), it represented 17% of dementia patients who were under age 70 years at death. More recently, a neuropathological review of 382 cases from the State of Florida Brain Bank7 showed that FTD constituted 5% of the total but 8% of those cases under the age 70 years. Two groups have attempted to determine the clinical