There are two different phenotypes of multiple sclerosis (MS) in Asians: opticospinal (OSMS) and conventional (CMS). In Japan, four nationwide surveys of MS have been performed. The first three were in 1972, 1982 and 1989, and we conducted the fourth in 2004. Based on clinically estimated sites of lesions, 1,493 patients with clinically definite MS were classified as having CMS (57.7%), optic-brainstem-spinal MS (5.8%), brainstem-spinal MS (4.6%), OSMS (16.5%), spinal MS (10.6%) or unclassified MS (4.9%). The latest survey revealed the following: a four-fold increase in the estimated number of clinically definite MS patients in 2003 (9,900; crude MS prevalence, 7.7/100,000) compared with 1972; a shift in the peak age at onset from the early 30s in 1989 to the early 20s in 2003; a successive proportional decrease in optic-spinal involvement in clinically definite MS patients; a significant north-south gradient for the CMS/OSMS ratio; after subdivision of the mainland (30-45° North) into northern and southern parts at 37°N, northern-born northern-residents showed a significantly higher CMS/OSMS ratio and higher frequency of brain lesions fulfilling the Barkhof criteria (Barkhof brain lesions) than southern-born southern-residents; among northern patients, the absolute numbers of CMS patients and those with Barkhof brain lesions rapidly increased with advancing birth year. Based on MRI findings, MS patients were further subdivided into those with OSMS with or without longitudinally extensive spinal cord lesions extending over three or more vertebral segments (LESCLs) and those with CMS with or without LESCLs. Although disease duration did not differ significantly among the four groups, EDSS scores were significantly higher in patients with LESCLs than in those without, irrespective of OSMS or CMS phenotype. Similar trends were found for the frequencies of bilateral visual loss, transverse myelitis, and marked CSF pleocytosis and neutrophilia. Increased IgG index, frequencies of brain lesions fulfilling the Barkhof criteria and secondary progression were more commonly found in CMS patients than in OSMS patients, while negative brain MRIs were more commonly encountered in OSMS patients than CMS patients, irrespective of the presence of LESCLs. These findings suggest that MS phenotypes are drastically changed by environmental factors, such as latitude and “Westernization”, and that demographic features not only vary based on CMS or OSMS phenotype, but also with the presence or absence of LESCLs.