The neurofilament is the major cytoskeletal structure of myelinated axons. In this study, CSF levels of the light subunit of the neurofilament protein (NFL) were increased in patients with vascular dementia (VAD), AD, and frontotemporal dementia (FTD) compared with neurologically healthy individuals. Because NFL is localized mainly in myelinated axons, these results suggest that the degeneration of white matter in these disorders causes the increased CSF NFL levels.