In November 1999 the Department of Health introduced a national vaccination programme using newly licensed meningococcal serogroup C conjugate vaccines (MenC). In the largest national mass vaccination campaign ever undertaken in the UK, all people under the age of 18 years are being oVered vaccination: three doses for infants as part of the primary vaccination schedule at 2, 3, and 4 months of age; two doses for infants age 4–12 months; and one dose for individuals aged 1–18 years. The cost to the government has not been made public. Vaccination started a year earlier than originally planned and the UK is the only country thus far to have licensed and introduced the vaccine. Prior to the campaign there was no experience of using the vaccine outside the setting of a clinical trial. What is the rationale behind this ambitious programme and what unanswered questions remain?