Previous diagnostic guidelines for MS relied largely on clinical evidence and cerebrospinal fluid analysis. In 2001, guidelines were published that allowed partial substitution of the required clinical evidence by magnetic resonance imaging findings and defined primary progressive multiple sclerosis (PPMS). Recently, revised guidelines on MS diagnosis were published, mainly to improve definitions of dissemination in space (using spinal cord imaging) and in time (using T2 lesions), enabling a faster and more accurate MS diagnosis. Criteria for PPMS were also revised. Current research is concentrating on the definition of uniform clinical terms, to allow a more standardized diagnosis, and aims to simplify the criteria while improving diagnostic accuracy.