We investigated CA2/3 ubiquitin-immunoreactive neurites in 120 cases of diverse neurodegenerative diseases. This neuritic change occurred in 25 of 30 cases of Alzheimer's disease (AD) with coexistent Parkinson's disease (PD) changes, as well as two cases of PD and two cases of progressive supranuclear palsy. All 29 cases with neuritic change showed cortical Lewy bodies. Neuritic change was absent in 86 cases of neurodegenerative diseases without Lewy bodies, including 66 cases of pure AD. Thus, ubiquitin-immunoreactive CA2/3 neurites and cortical Lewy bodies, frequently coexist; this association appears to be independent of the presence or absence of coexistent pathologies, eg, AD. Moreover, in and of itself, nigral degeneration without Lewy bodies, such as that encountered in other (non-PD) movement disorders, apparently is not associated with CA2/3 neuritic change.