Cough is a frequent reason for ED consultation. When one considers the epidemiological data, whooping cough must be considered in the differential of subacute cough. Clinical symptomatology is slightly different in the adult and unvaccinated child. An infection by Bordetella pertussis should be suspected when the history shows a persistent cough for more than 1 week in conjunction with other clinical elements. Several methods are available to establish a diagnosis: culture, PCR and bacterial serology. An early diagnosis will allow effective treatment, limit the transmission to unvaccinated infants, reduce complications and prevent extensive and expensive check-ups for chronic cough.