We herein report two patients with dementia with Lewy bodies (DLB) presenting characteristic symptoms suggestive of the behavioural variant of frontotemporal dementia (bvFTD). Patient 1 presented behavioural and personality changes from the onset, such as restlessness, compulsive behaviours, and stereotypical speech. A neuroimaging study showed preferential frontal involvement, and this patient fulfilled the diagnostic criteria for bvFTD. However, 123I‐metaiodobenzylguanidine cardiac scintigraphy revealed a markedly lowered uptake, suggesting the diagnosis of possible DLB. Patient 2 fulfilled the criteria for probable DLB, but later presented bvFTD‐like symptoms similar to those in patient 1. These patients suggest that DLB can be a candidate for differential diagnosis of bvFTD in the clinical setting.