In January 2006, an outbreak of hepatitis A occurred in a socio-economically deprived area of Liverpool, in the United Kingdom (UK), where extensive community outbreaks of hepatitis had previously occurred. A total of nine cases were confirmed. Five of these were linked within a primary school. The outbreak initially occurred among a close social contact group, but there was evidence of subsequent person-to-person transmission within a local primary school. The school was attended by 221 pupils (age range 4-12 years) with a total of 37 teaching and other staff (age range 22-71 years). Following local risk assessment, mass hepatitis A virus (HAV) vaccination was offered to all staff and pupils, as all were judged to be likely to have been in close contact with the affected pupils. A total of 188 of 217 eligible children (87%), and 33 of 37 staff (89%) were vaccinated. A salivary seroprevalence survey was conducted at the same time as vaccination to assess the benefit of this intervention in the school population. The survey confirmed high levels of susceptibility to hepatitis A in this setting (97.8%, 95% CI 91.6 to 99.62). The direct costs of intervention were estimated as euro5,000. The cost effectiveness of intervention varies widely (euro60.50 to euro2,099 per case avoided) depending on the expected attack rate, which is difficult to estimate due to heterogeneity in published studies.