We report a 68-year-old woman who developed progressive dementia and parkinsonism. She was well until 1990 when she was 58 years of age. She started to show memory loss. Four years later, she developed difficulty in dressing and behavioral problems such as eating rice with her hands, going out of her house without purposes, and difficulty in finding the rest room in her house. She was admitted to the neurology service of Hatsuishi Hospital on January 19, 1996, when she was 64 years of the age. On admission, she was alert but markedly demented. The score of Hansegawa Dementia Scale was 0/30. She was unable to make any coherent conversation. She appeared to have dressing apraxia but did not appear to have aphasia. Cranial nerves were intact. She walked in small steps with stooped posture. She did not have motor weakness but she showed plastic rigidity in all four limbs. No tremor or ataxia was noted. Deep tendon reflexes were within normal limits but the plantar response was extensor bilaterally. She continued to deteriorate after admission. In May of 1998, she started to fall. In June of 1998, she had a generalized convulsion. In January of 1999, she became unable to take foods orally and a gastrostomy was placed. She expired on May 29, 1990. She was discussed in a neurological CPC and the chief discussant arrived at the conclusion that the patient had Alzheimer's disease. The question was whether her parkinsonism was a part of her Alzheimer's disease or she had an additional disease to explain her parkinsonism. Post-mortem examination revealed moderate to marked atrophy of the frontal and the temporal lobes as well as in the limbic areas with dilatation of the lateral ventricles. Marked neuronal loss was noted in the CA 1 to the subiculum region with gliosis. Neurofibrillary tangles were seen in the remaining neurons. Neuropil threads were seen by Gallyas-Braak staining. Similar changes were seen in the parahippocampal gyrus and in the entorhinal cortex. Senile plaques were seen in the insular cortex and in other cortical areas. Cortical type Lewy bodies were seen in the cingulate cortex. The Meynert nucleus showed marked neuronal loss and gliosis. The substantia nigra and the locus coeruleus showed moderate loss of pigmented neurons. Lewy bodies were seen in these regions. The dorsal motor nucleus of the vagal nerve was retained, however, one Lewy body was observed. Pathologic diagnosis was Alzheimer's disease plus Parkinson's disease. It is an interesting question whether or not her parkinsonism was due to nigral lesion or frontal lesions. It is known that parkinsonism may complicate in advanced Alzheimer's disease not necessarily due to nigral lesion. On the other hand, in incidental Lewy body disease, the substantia nigra shows mild Parkinson's disease-like change without clinical parkinsonism. This patient appeared to have been a true complication of Alzheimer's disease and Parkinson's disease.