This article reviews the applications of functional neuroimaging with positron emission tomography (PET) and single photon emission computed tomography (SPECT) to the diagnosis and treatment of Parkinson's disease (PD). PET measurements with [18F]deoxyglucose to measure glucose metabolism or with various markers of the pre- and postsynaptic dopamine systems may distinguish idiopathic PD from other conditions presenting with an akinetic-rigid state. Moreover, PET has been used to gain new insights into mechanisms of cell death and the role of heredity in Parkinson's disease. Finally, we discuss the use of functional neuroimaging to study the role of the basal ganglia in movement and cognition in PD.