Pertussis (i.e., whooping cough) is associated typically with an inspiratory "whoop," prolonged paroxysmal cough, and posttussive vomiting; however, persons infected with Bordetella pertussis sometimes experience atypical symptoms, making prompt recognition difficult and probably increasing infection transmission. All infants aged <6 months and any infants who have not yet received 3 doses of diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine are especially vulnerable to B. pertussis infection. This report summarizes the investigations of two pertussis deaths that occurred in 2000. Clinicians should consider pertussis as a cause of illness, especially among vulnerable infants who present with cough illness, respiratory distress, or apnea. Timely diagnosis of pertussis in caregivers and other contacts of infants could prevent infant pertussis fatalities.