Positron emission tomography (PET) imaging in clinical neurology serves several purposes: differential diagnosis, especially in the early stage of neurologic disorders, description of pathophysiologic changes that are responsible for manifestation and course of a disease, and evaluation and follow-up of treatment effects. Many of these applications are possible with the most widely available PET tracer, 2-deoxy-2-[18F]fluoro-D-glucose (FDG). Additional tracers are used clinically to detect the disturbance of specific neurotransmitter and receptor systems, blood flow, oxygen metabolism, and amino acid uptake. Main diagnostic issues addressed in this review are early diagnosis of Alzheimer's disease and other dementias, differential diagnosis of movement disorders, diagnosis of recurrent brain tumors, identification of viable tissue in ischemic stroke, and localization of epileptogenic foci. Techniques for presurgical localization of eloquent cortex and monitoring of therapy are presented.