Modalities for imaging morphology do not contribute significantly to the differential diagnosis of movement disorders. In contrast, functional imaging as PET or SPECT can differentiate among Parkinson's disease (PD), vascular or toxic Parkinsonism and movement disorders within multi system degeneration. Especially the decreased DOPA uptake--detected by 18F-DOPA or 123I-beta CIT--within the striate with accentuation in the posterior putamen is typical for PD, where initially D2-receptor activity--imaged by 11C-raclopride or 123I-iodobenzamide--is increased. In contrast to this typical pattern dopaminergic terminals as well as D2-receptors are diffusely reduced in multi system degeneration, where often energy metabolism is additionally disturbed. In Parkinson syndrome of vascular origin focal disturbances of pre- and postsynaptic dopaminergic sites and energy metabolism are found, movement disorders after intoxication are accompanied by selective loss of dopaminergic neurons (MPTP) or by widespread neuronal damage in the basal ganglia as well as in the cortex (Cyanide, solvents). Functional studies additionally permit the follow-up of disease progression, by which also the efficacy of therapeutic strategies can be assessed.