A cluster of three measles cases occurred at the Gendarmerie of Rambouillet in March 2011. A survey conducted among 170 subjects highlighted the difficulty of gathering information about patients (previous infection or vaccination) and of planning the vaccination of non-immune contacts. The study also found that the proportion of immunized patients increased from 25% to 43% after one vaccination. The disappointing results highlight the public health role of family practitioners involving in informing and vaccinating patients before measles epidemics occur.