Perfusion CT or MRI have been extensively developed over the last years and are accessible on most imaging machines. Perfusion CT has taken a major place in the assessment of a stroke. Its role has to be specified for the diagnosis and treatment of the vasospasm, complicating a subarachnoid hemorrhage. Perfusion MRI should be included in the assessment of any brain tumor, both at the time of the diagnosis as well as in the post-treatment monitoring. It is included in the multimodal approach required for the optimum treatment of this disease. The applications in epilepsy and the neurodegenerative diseases are in the evaluation process.