Introduction - On February 11, 2008, the reporting of three cases of measles among residents of the Reims metropolitan area triggered an investigation to document the outbreak, assess its scope, and implement appropriate control measures. Methodology - Active case finding was conducted among all physicians practicing in Reims (private practitioners, school doctors, hospital doctors, and emergency medical services). The clinical case definition for measles was that of the WHO. Biological confirmation was performed by detecting specific IgM antibodies, IgG seroconversion, or viral RNA in serum or saliva samples. Genotyping and phylogenetic analysis were conducted. Clinical and epidemiological data were collected for each case. At the Reims University Hospital, a crisis unit was established to determine on a case-by-case basis the appropriate course of action for patients and healthcare workers who had been in contact with them. Results - Between January 21 and March 25, 2008, 19 cases of measles, including 6 nosocomial cases, were identified in Reims and its metropolitan area. These cases involved 11 adults (ages 19–46) and 8 children (ages 7 months–14 years). Among the 8 children, 3 were unvaccinated and 2 had received only one dose of the vaccine. Among the 11 adults, 7 were eligible for vaccination. Ten cases were hospitalized or presented to the emergency department, and 3 of them developed complications. A transmission chain involving 15 cases was identified, spanning 3 generations of cases. The same D4 genotype was identified in 9 of the 15 cases, while the D5 genotype was found in an isolated community case. Discussion - This episode highlighted the value of comprehensive measles surveillance in France for detecting clusters of cases and the need for rapid virological diagnosis. In this regard, the use of saliva-based IgM detection kits proved highly useful. However, difficulties in controlling the occurrence of cases were observed. It should be noted that unvaccinated adolescents and young adults who have not been exposed to the virus (particularly among hospital staff, including interns) currently constitute a reservoir of susceptible individuals who could trigger outbreaks. The recent update of vaccination recommendations has, moreover, taken this into account. (R.A.)