Although cognitive impairments seen in early and mild stages of Alzheimer Disease (AD), Vascular Dementia (VaD) and Lewy Bodies Dementia (LBD) might overlap, they have quite different aspects. The prominent cognitive impairments in AD are in the episodic and semantic memory. In VaD, while cognitive flexibility, initiation, goal formulation and mood changes deteriorate, memory performance is preserved compared to these functions. On the other hand, the main impairments in LBD are cognitive fluctuation, attention, visual-spatial abilities and visual memory, whereas the verbal memory components are preserved.