The diagnosis of Multiple Sclerosis (MS) is based on a careful evaluation of clinical history, on neurological exam and paraclinical tests aimed at identifying temporal and spatial dissemination of demyelinating lesions of the Central Nervous System; on the other side, it is mandatory to exclude any other possible disease able to better explain clinical symptoms. In 2001 diagnostic criteria revised in 2005 and more recently in 2010 have been elaborated to define clinical and paraclinical evidences necessary for the diagnosis of MS; instrumental exams include Magnetic Resonance Imaging (MRI), cerebrospinal fluid analysis and visual evoked potentials. MRI is necessary to demonstrate dissemination in time and space of demyelinating lesions.