We report three presenile patients who were initially suspected of having Alzheimer's disease (AD) or being in the prodromal stage of AD, regardless of visuoperceptual dysfunctions in daily living, because they lacked the core features and prodromal non-motor symptoms of dementia with Lewy bodies. Subsequently, progression to dementia with Lewy bodies was suspected based on neuropsychological and neuroimaging findings; additionally, one of the three patients suffered from visual hallucinations. Neuropsychological examinations such as subjective contours, cube copying and block design in the Wechsler Adult Intelligence Scale-III revealed visuoperceptual dysfunction in all three patients even when other cognitive functions were rather preserved. Brain magnetic resonance imaging revealed no significant brain atrophy, including in the parieto-occipital area and the hippocampus, while brain 18F-fluorodeoxyglucose positron emission tomography demonstrated right dominant metabolic reductions in the occipital lobe, including the primary visual cortex, in all three patients. We suggest the possibility of progression to dementia with Lewy bodies, but not AD or posterior cortical atrophy. Regardless of the presence of core features and prodromal non-motor symptoms, this progression is suggested when there are difficulties only in higher-level visual processing such as subjective contours and block design in the Wechsler Adult Intelligence Scale-III, no significant atrophy of the parieto-occipital area and hippocampus on brain magnetic resonance imaging, and hypometabolism in the occipital lobe including the primary visual cortex on brain 18F-fluorodeoxyglucose positron emission tomography.