Parkinson's disease (PD) is a common disorder, and the diagnosis of Parkinson's disease is clinical and relies on the presence of characteristic motor symptoms. The accuracy of the clinical diagnosis of PD is still limited. Functional neuroimaging using SPECT technique is helpful in patients with first signs of parkinsonism. The changes detected may reflect the disease process itself and/or compensatory responses to the disease, or they may arise in association with disease- and/or treatment-related complications. This paper addresses the value of SPECT in early differential diagnosis of PD and its potential as a sensitive tool to assess the pathophysiology and progression, as well as the therapeutic efficacy of PD.