OBJECTIVE To investigate the current prevalence of Helicobacter pylori infection in childhood, the risk factors for infection, and the effect of infection on growth in preadolescent schoolchildren. METHODS Population based sample of 7 year old schoolchildren followed up at age 11; data on risk factors for infection collected at age 7; presence of infection at age 11 determined by measurement of salivary IgG against H pylori by a newly developed enzyme linked immunosorbent assay (ELISA). Height was measured at 7 and 11 years of age. METHODS 554 schoolchildren from Edinburgh. RESULTS 62 (11%) children had H pylori infection. Independent risk factors for infection were single parent families (adjusted odds ratio = 2.5; 95% confidence interval 1.1 to 5.7), the 10% most crowded homes (3.1; 1.3 to 7.2), and schools serving predominantly rented housing estates (2.5; 1.0 to 6.5). School catchment area was more important than parental social class or housing tenure. Growth in height between 7 and 11 was diminished in infected children by a mean of 1.1 cm (0.3 to 2.0 cm) over four years. This growth reduction was largely confined to girls (1.6 cm over four years), among whom it correlated with salivary IgG (P = 0.015). CONCLUSIONS Data from salivary assay to investigate the epidemiology of H pylori suggest that factors relating to the type of community in which the child lives may now be as important for acquisition of this infection as features of the family home. The greater reduction of growth among infected girls raises the possibility that H pylori infection may delay or diminish the pubertal growth spurt.