Japanese Society of Neurology (JSN) was established in 1960 with 643 members, and in 2009 it has grown up to a big society having more than 8,000 members including 3,600 neurology board specialists. JSN has greatly contributed in elucidating and resolving many socio-medical problems. I will take three topics including SMON (subacute myelo-optico-neuropathy), infectious Creutzfeldt-Jakob disease (CJD) and Minamata disease. SMON was a new epidemic disease characterized by subacute optic neuritis and myeloneuropathy associated with diarrhea and abdominal symptoms. The research committee clarified that it was a neurological complication of chinoform, a drug for gastroenteritis. CJD surveillance started in 1996 for variant CJD, and uncovered many patients who developed CJD after human dura draft. The government prohibited to use non-inactivated human dura. Minamata disease is an organic mercury poisoning of people who took fish contaminated by mercury in Minamata bay in Kumamoto or in Aganogawa river in Niigata. The factories discharged water contaminated with mercury which was accumulated in fish and shellfish. Still many victims claim for compensation to the companies and government. Neurologists in Kumamoto and Niigata greatly contributed to diagnose and treat the victims and to clarify the cause of the disease.