Objective: To describe a case of early-onset Alzheimer's disease (AD) in an apolipoprotein (Apo) epsilon 2/epsilon 2 homozygote. Background: Apo epsilon 2/epsilon 2 is the rarest of the ApoE genotypes, representing only 1.4% of the population. Cognitive decline in ApoE epsilon 2 homozygotes has rarely been reported. Case Report/Methods: We report a 58-year-old Apo epsilon 2/epsilon 2 female who meets clinical criteria for probable AD as confirmed by neuropsychological testing, positron emission/computed tomography scan, CSF analysis and genetic screening for known mutations. Results: The clinical course is typical of AD, with progressive cognitive and functional decline. Conclusion: Clinically confirmed early-onset AD is atypical in ApoE2 homozygotes but can occur. Copyright (C) 2010 S. Karger AG, Basel