The records-linkage system of the Rochester Epidemiology Project was used to ascertain incident cases of frontotemporal lobar degeneration (FTLD) in Rochester, MN, from 1990 through 1994. Four cases of FTLD were identified (all women); two were confirmed neuropathologically. All were of the behavioral-dysexecutive type and had onset before age 70. The incidence rates (new cases per 100,000 person-years) were 2.2 for ages 40 to 49, 3.3 for ages 50 to 59, and 8.9 for ages 60 to 69. For comparison, the corresponding rates for Alzheimer disease were 0.0, 3.3, and 88.9.