Parkinson disease (PD) is associated with nigral degeneration and striatal dopamine deficiency. Demonstrating midbrain structural abnormalities with transcranial sonography or diffusion-weighted MRI or showing striatal dopamine terminal dysfunction with PET or SPECT supports the diagnosis and rationalizes the use of dopaminergic medications. In atypical PD variants, transcranial sonography can detect striatal hyperechogenicity, and diffusion-weighted imaging can detect increased putamen water diffusion, whereas (18)F-FDG PET reveals reduced lentiform nucleus glucose metabolism. PET and SPECT can detect changes in striatal dopamine levels after levodopa administration and relate these to motor responses. Loss of cortical dopaminergic and cholinergic function is present in demented PD and, on occasion, amyloid deposits can be detected. Loss of cardiac sympathetic innervation can be sensitively detected in PD with (18)F-dopamine PET or (123)I-metaiodobenzylguanidine SPECT. Finally, PET can detect widespread brain inflammation in PD. This review discusses the role of structural and functional imaging for diagnosing and managing different parkinsonian syndromes.