An epidemiologic survey of JCA was carried out in two regions of France, the western part of Paris and Brittany, differing in terms of geological background and demography. The prevalence was 0.77 and 0.100% and the incidence 0.019 and 0.013%, respectively. The type of onset, the course of the disease, the immunological data and the degree of final disability were similar in both regions. These data were compared to other studies and the factors of possible discrepancy analysed.