Mycoplasma pneumoniae is transmitted from person to person via aerosols and causes acute respiratory infections, including pharyngitis, tracheobronchitis, and pneumonia. Several Mycoplasma pneumoniae outbreaks have been reported in closed or semi-closed settings (military camps, hospitals, religious communities, institutions) with attack rates that are sometimes very high, reaching 25 to 71%. Mycoplasma pneumoniae pneumonia is the leading cause of community-acquired pneumonia in children aged 5 to 15 years. On June 20, 2005, the Loiret Departmental Health and Social Services Agency (DDASS) alerted the Central-West Interregional Epidemiology Unit (CIRE) to the occurrence, over a period of several weeks, of approximately twenty cases of pneumonia of unknown etiology among children attending preschool and elementary schools in a town within the department. The initial alert came from general practitioners. An epidemiological, clinical, and microbiological investigation, initiated by the Cire and the InVS, was launched to confirm and describe the outbreak, identify the cause, and determine, if necessary, the control measures to be implemented. The various stages of the investigation were explained to the students’ parents during a meeting with the DDASS, the school health service, and the CIRE. Serological analyses identified Mycoplasma pneumoniae as the causative agent. A meeting to present the results of the investigation was held in the fall of 2005.