The study of 414 measles cases, admitted in several childrens' hospitals in the Lyons area, underlines the important cost of this disease. Moreover, the occurrence of complications (in 56% of children hospitalized with measles), some of which as severe as encephalitis (n = 9) and/or death (n = 4), shows that an improvement of preventive measures is indispensable. Vaccination appears to be the most effective way, but the actual immunization level remains insufficient in France. This situation could be optimized either by intensifying the sensibilization fields or by rendering vaccination compulsory before entrance to school and collectivities.