We describe an autopsy-proven case of Parkinson's disease with dementia showing early-onset delusions and hallucinations with limbic-type Lewy body pathology. A Japanese man 72 years old at time of death, developed hand tremor at the age of 45. On neurological examination at 47 years of age, parkinsonian symptoms and signs were present. Pergolide mesylate 1000 μg/day improved his motor symptoms. Then, delusional jealousy appeared and he consulted the psychiatric department in our hospital at the age of 50. Pergolide mesylate 2000 μg/day and trihexyphenidyl hydrochloride 6 mg/day were prescribed. His delusional jealousy made him hit his wife at the age of 63, and visual hallucinations were demonstrated. Brain magnetic resonance imaging (MRI) at the age of 65 revealed mild frontal lobe atrophy. At the age of 72, apparent dementia and dysphagia appeared. The total clinical course was 27 years. The brain showed mild frontal atrophy and weighed 1295 g before fixation. Depigmentation of the substantia nigra and locus ceruleus was macroscopically apparent. Neuronal loss with gliosis was noteworthy in the substantia nigra, locus ceruleus, dorsal vagal nucleus, nucleus basalis of Meynert (NBM), and intermediate lateral nuclei; however, cerebral neocortex and limbic systems were relatively preserved. Widespread occurrence of Lewy bodies with a few Lewy neurites were demonstrated (limbic-type). Noticeable Lewy body pathology in the NBM was shown in contrast to that in other limbic system structures, such as the amygdala and parahippocampal gyrus, and cerebral cortex. In vivo structural imaging studies revealed that cholinergic projections from the NBM could be responsible for generation of cholinergic deficiency syndrome, including delusions and hallucinations. Furthermore, basal forebrain volume is reduced in patients with Parkinson's disease showing visual hallucinations. Prominent Lewy body pathology in the NBM could be related to not only visual hallucinations but also delusions.