The clinical diagnosis of Parkinson's disease is based on the identification of some combination of the clinical motor signs of bradykinesia, rigidity, tremor and postural instability. Three levels of diagnostic confidence are differentiated: possible, probable, and definite. The diagnosis of possible and probable Parkinson's disease based on clinical criteria alone, while definite diagnosis requires neuropathologic confirmation. To differentiate Parkinson's disease (idiopathic Parkinsonian syndrome) and other Parkinsonian syndromes is of increasing importance considering the therapy and life expectancy of the patients. Recently the functional imaging technics have been more and more helpful in the early differential diagnosis of Parkinson's disease.