Differentiation of "dementia with Lewy body pathology" (DLB) and delirium may be problematic in some cases, due to some of their common clinical characteristics such as fluctuations and hallucinations. Longer duration of cognitive changes usually aids in DLB diagnosis. However, presentation of DLB with an abrupt onset as a prolonged confusional state and hallucinations is also, even if rarely, described. We report the case of an elderly patient with probable dementia with Lewy body pathology, presenting with a prolonged acute confusional state, in order to draw attention to its diagnostic difficulty and the importance of careful target-oriented anamnesis in such cases. This type of dementia should be included in the differential diagnosis of elderly patients presenting with otherwise unexplained prolonged acute confusional states.