Background. We conducted a population-based, nation-wide, prospective study to identify who introduced pertussis into the household of infants aged ⩽6 months admitted to the hospital for pertussis in the Netherlands. During the period 2006–2008, a total of 560 household contacts of 164 hospitalized infants were tested by polymerase chain reaction, culture, and serological examination to establish Bordetella pertussis infection. Methods. Clinical symptoms and vaccination history were obtained by a questionnaire submitted during sample collection and 4–6 weeks afterwards. Results. Overall, 299 household contacts (53%) had laboratory-confirmed pertussis; 159 (53%) had symptoms compatible with typical pertussis infection, and 42 (14%) had no symptoms. Among children vaccinated with a whole-cell vaccine, 17 (46%) of 37 had typical pertussis 1–3 years after completion of the primary series, compared with 9 (29%) of 31 children who had been completely vaccinated with an acellular vaccine. For 96 households (60%), the most likely source of infection of the infant was established, being a sibling (41%), mother (38%), or father (17%). Conclusions. If immunity to pertussis in parents is maintained or boosted, 35%–55% of infant cases could be prevented. Furthermore, we found that, 1–3 years after vaccination with whole-cell or acellular vaccine, a significant percentage of children are again susceptible for typical pertussis. In the long term, pertussis vaccines and vaccination strategies should be improved to provide longer protection and prevent transmission.