Introduction: Haemophilus influenzae type B has been the pathogen responsible for a significant proportion of cases of septic arthritis in children in the past. Vaccination was introduced in the United Kingdom in October, 1992 in order to combat meningitis and epiglottitis. This study looks at the effects of vaccination on childhood septic arthritis in Wales. Methods: Data was collected prospectively from 1988 by the Public Health Laboratory Service in Wales. Data was analysed with a two-sample t-test. Results: There were 17 cases in children in which 16 were attributed to type B. 14 cases occurred in the 5 years before mass immunisation. Only 2 cases occurred in the 8 years following immunisation. The incidence of Haemophilus influenzae septic arthritis in children has fallen significantly since the introduction of immunization (P=0.009). Discussion: Vaccination has resulted in a significant fall in the incidence of Haemophilus influenzae type B septic arthritis in children in Wales. This may have consequences on guidelines for the empirical treatment of septic arthritis. If a child if found to have Haemophilus influenzae septic arthritis, this is suspicious of immunocompromise, or an alternate type infection. The novel way in which infection has been controlled may be one which can be used in future to control multi-resistant bacterial infection in orthopaedic surgery.