The prevalence of active infection with Helicobacter pylori in the general population of England and Wales was estimated using high reactivity for specific IgG in serum ELISA as a marker. A total of 10118 anonymized residues of serum samples collected in 1986 and 1996 from persons aged 1–84 years were used. Estimated prevalence of active infection varied by region and was highest in London. Prevalence was related to decade of birth and increased from 4·3% in those born during the 1980s to 30% in those born before 1940. An estimated total of 7·5 million people living in England and Wales have an active infection and analysis by decade of birth showed no significant difference between samples collected in 1986 and 1996. These data suggest H. pylori infection is becoming less common, is acquired at an early age and is unlikely to be resolved unless suitable antimicrobial treatment is sought.