OBJECTIVE: To establish the likely health and cost impacts of a pre-school booster vaccination for Bordetella pertussis, when added to existing UK primary vaccination schedules assuming that a diphtheria, tetanus, and acellular pertussis, (DTPa) booster would replace the current diphtheria and tetanus (DT) booster. METHODS: A transition state model of pertussis infection in a closed population representative of England and Wales, comprised of eight age bands with susceptible, infected and immune population sub-groups. Herd-immunity was explicitly modeled. Epidemiological service use and cost data were sourced from routine statistics, published literature and, where necessary, clinical estimates. The number of pertussis cases, hospitalisations and deaths were forecast for a five-year period. Quality of life gains were not explicitly calculated. RESULTS: Introducing a pre-school pertussis booster and achieving 84% coverage is predicted to cost an additional £14.32m over a five-year period, assuming £5 marginal cost between DTPa and DTP or £8.60m assuming a £3 marginal cost. Offset against this are the cost of reduced hospitalisations and GP consultations, which are expected to total between £4.21m and £4.60m. The return on this investment would be a reduction in up to 1,700 hospitalisations, between 5,000 and 27,000 pertussis cases depending on the level of under-reporting and assuming a vaccine waning period , and one infant death. CONCLUSIONS: The introduction of a pre-school booster is predicted to significantly reduce the number of hospitalisations and pertussis cases contracted. The estimated marginal cost of this strategy is £10m over a five-year period, assuming a £5 difference between DTP and DTPa or £4m, were the difference only £3.