Parkinson's disease (PD) is a common neurodegenerative disorder. In 2015, The Movement Disorder Society Clinical Diagnostic Criteria for PD was published. In the criteria, the absolute exclusion criteria and red flags were designed to minimize diagnostic error, in particular to differentiate from neurodegenerative or secondary parkinsonism. Here, we reviewed neurodegenerative disorders that we should differentiate from PD. The common differential diagnoses, such as multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies, and essential tremor are important but sometimes difficult to differentiate. We also described the features of rare but important differential diagnoses: neuronal intranuclear inclusion disease, Perry syndrome, Fragile X tremor/ataxia syndrome, Huntington's disease, dopa-responsive dystonia, Wilson disease, and neurodegeneration wit,1 brain iron accumulation.