In England and Wales, routine monitoring has been consistently showing an increase in mortality and morbidity due to infection with the Hepatitis C Virus (HCV). However, the magnitude of the underlying epidemic is still the subject of debate. In this paper we present estimates of the number of individuals aged 15—59 chronically infected with HCV in 2003, derived from a Bayesian synthesis of information available from multiple sources on the size of the groups at risk for HCV and the risk specific anti-HCV prevalence. Results show that the number of chronic infections is of the order of 142,000 (95% CrI: 90,000, 231,000), with the majority (85%, 95% CrI: 74%, 93%) in injecting drug users and about 80% (95% CrI: 74%, 84%) in the age group 15—44.