Many people confuse the cognitive impairment of Parkinson’s disease with dementia, but the two are not the same thing. The decline in cognitive status due to Parkinson’s disease affects more attention, executive function and visual-spatial ability, and memory perception, such as difficulty drawing shapes like cubes. Alzheimer’s, on the other hand, affects more memory, often forgetting recent events, not being able to find home, etc. It is possible for people with Parkinson’s disease to develop dementia symptoms. Parkinson’s disease dementia is the severe stage of Parkinson’s disease cognitive impairment, while Parkinson’s disease mild cognitive impairment is the stage between normal Parkinson’s disease cognitive function and Parkinson’s disease dementia. So which Parkinson’s disease patients are more likely to develop dementia? Advanced age: Age is the most critical factor. In contrast, dementia is less common in patients with early-onset PD. In particular, dementia is less likely to occur in patients with onset before the age of 40. Longer disease duration: The longer the disease duration and the more severe the disease progression, the more likely dementia will occur. If dementia develops within a year of having Parkinson’s disease, we need to re-evaluate whether it is primary Parkinson’s disease or another condition such as Lewy body dementia. Drug relationship: Memory loss and cognitive impairment due to Parkinson’s disease drugs often appear soon after taking the drug and are closely related to the duration of drug use. Dementia in Parkinson’s disease itself appears gradually as the disease progresses. Drugs used to treat Parkinson’s disease such as anticholinergic drugs, amantadine, and dopamine agonists are all likely to cause mental cognitive impairment, with anticholinergic drugs in first place. The corresponding mental cognitive impairment soon after taking the medication should be considered drug-related. Patients with severe motor symptoms of Parkinson’s disease: tonicity, postural instability and gait disturbance (PIGD subtype) predominate and are more likely to develop dementia. Mild cognitive impairment early on: Patients with Parkinson’s disease with cognitive impairment early on are more likely to develop symptoms of dementia. Conversely, if early intelligence is better, dementia is less likely to occur in the distant future.