In Europe, France is located between high and low risk areas of Multiple Sclerosis (MS). We estimated the national prevalence of MS in France on 31st October 2004 and the incidence between 2000 and 2007 based on data from the ‘Caisse Nationale d’Assurance Maladie des Travailleurs Salariés’ which insures 87% of the population. MS like other chronic diseases is one of the 30 long-term illnesses (Affections de Longue Durée, ALD). We analysed geographic variations in the prevalence and incidence of MS in France using the Bayesian approach.Total MS prevalence in France standardised for age was 94.7 per 100,000; 130.5 in women; 54.8 in men. The notification rate for MS (2000-2007) after age-standardisation according to the European population was 6.8 per 100,000; 9.8 in women and 3.7 in men. With a Bayesian approach, the prevalence of MS was higher in northeast and lower in the Paris area and on the Mediterranean coast. The notification rate was higher in northeast and lower on the Atlantic coast and in the Alps as well as on both sides of the Rhône River.The study of other chronic diseases for which ALD status was registered before MS revealed that comorbidities were rare, essentially represented by psychiatric diseases (40.2%) and diabetes (20.3%).This study is performed among a representative population using the same method throughout. The Bayesian approach which takes into account spatial heterogeneity and spatial autocorrelation did not confirm the existence of a clear gradient but only higher or lower areas of MS. The better knowledge of MS epidemiology will allow to venture hypothesis its etiological factors.
