On August 27, 2013, the nurse coordinator at a long-term care facility for the elderly (Ehpad) in the Bouches-du-Rhône department reported two cases of acute respiratory infection with suspected pertussis among residents to the Regional Health Agency. An epidemiological investigation was conducted: case definitions were established, laboratory test results and control measures implemented were reviewed, and staff vaccination status was recorded. The investigation identified 26 cases of pertussis that occurred between July 25 and September 8. Of these cases, 3 were biologically confirmed by the National Reference Center for Pertussis and Other Bordetellosis. The index case was a nursing assistant at the nursing home, who infected the first residents as well as her 3-month-old granddaughter, through whom the diagnosis of pertussis was actually made. Control measures were quickly implemented by the nursing home staff. Vaccination coverage among staff against pertussis was 18% and rose to 37% following a vaccination session organized at the nursing home by the occupational physician. This pertussis outbreak at this facility highlights the difficulty of diagnosing this disease, particularly in adults, from both clinical and biological perspectives. Added to this are the challenges of implementing control measures in a long-term care facility and the low level of staff awareness regarding the risk of pertussis.