The objective of the present study was to establish whether performance in an action fluency task is of value in the differential diagnosis of Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). After collecting normative data on performance in an action fluency task and a conventional animal fluency task in a cohort of French-speaking healthy controls, we assessed AD and DLB patients. Only the action fluency score differed significantly between the two demented groups, with DLB patients performing worse than AD patients. However, a composite action and animal fluency score was found to be more effective for discriminating between these two groups.