The study of the brain functional correlates of neurological diseases, benefiting from extraordinary technological advances in the last decade, allows the in vivo investigations of the modifications in brain function associated to pathological conditions. The main clinical issue addressed in this field is the differential diagnosis among the physiological modifications associated with dementia syndromes. In addition, neuroimaging studies of epilepsy, extrapyramidal disorders, normal and pathological ageing have played an important role in neuropathological and clinical research in neurology. Innovative aspects, such as in vivo studies of neurotransmitter function with PET, and cognitive activation in normals and patients using fMRI and PET, represent fundamental research tools in the field.