Pertussis is a highly contagious acute respiratory illness. Prior to the availability of the whole-cell pertussis vaccine in the late 1940s, pertussis was one of the most common infectious diseases of childhood in the United States and a major cause of infant morbidity and mortality. Although pertussis vaccination has resulted in a substantial reduction in the disease, the incidence has been steadily increasing since the 1990s. The clinical presentation of pertussis may be variable depending on the age and immunization status of the patient. The classic presentation includes a triad of symptoms: paroxysms of coughing; an inspiratory whoop following cough; and posttussive vomiting. Those most vulnerable are the ones not yet immunized and the ones most likely to transmit the illness who may not exhibit "classic" pertussis symptoms, delaying or preventing identification and treatment. Because pertussis carries known morbidity and mortality risks, prevention and early identification are paramount.