Pertussis, or "whooping cough," caused by the gram-negative pleomorphic bacillus Bordetella pertussis, is a highly contagious, potentially life-threatening respiratory tract illness that has re-emerged worldwide as a cause of substantial morbidity and mortality in infants, children, and adolescents, despite high vaccination rates. Increased awareness and reporting, in addition to the availability of better diagnostic tests, partially explain the recent resurgence of pertussis. However, waning immunity after childhood immunization has resulted in a growing pool of susceptible adolescents and adults who are capable of transmitting pertussis to vulnerable unvaccinated or incompletely vaccinated infants. An acellular pertussis vaccine booster for adolescents has been recommended in the United States and other industrialized countries. Active immunization and early diagnosis are crucial in the management of pertussis.