Background: Multiple sclerosis is an autoimmune chronic demyelinating disease of the central nervous system. It is the main cause of non-traumatic disability in young adults and its incidence is increasing the last years. For these reasons, it is a major health problem. Nowadays, its aetiology and pathogenesis are not well known. There is a need of performing new studies in order to get a better understanding of the disease and also to improve the present treatments or to find out new therapeutical targets. In the last years, there has been an increasing interest about the role of the microbiota in some autoimmune disorders and specifically, in the regulation of central nervous system disordersObjective: The aim of this study is to analyse the composition of gut microbiota in patients diagnosed of multiple sclerosis and compare the results with healthy subjects in order to investigate if there is a specific faecal microbiota profile associated with this diseaseStudy design: The design selected is a pilot case-control studyParticipants: Cases: Multiple Sclerosis patients diagnosed at the Neuroimmunology and Multiple Sclerosis Unit of Dr. Josep Trueta University Hospital. Controls: Healthy subjects selected from the census of Girona and age-sex matched in a 1:1 ratio with cases