A cross-sectional survey of 2044 Year I children enrolled in 24 primary schools was performed to determine the prevalence of tuberculosis (TB) infection. Of the 2044 children, 1458 (71 per cent) were Mantoux-tested and 1452 Mantoux reactions were read. Of the total, 6.5 per cent were Mantoux-positive; 17.8 per cent of overseas-born children and 2.8 per cent of Australian-born children were Mantoux-positive (relative risk for overseas-born 6.9, 95 per cent confidence interval 4.2 to 9.6). In the areas of Sydney where the study was conducted, there is a high prevalence of TB infection (non-contagious) among overseas-born children in the five- to seven-year age group. This indicates that there may be a large pool of infected children, a proportion of whom are at risk of developing active (contagious) adult-type TB in the future. These data, with other published data on TB infection rates in other age groups, can contribute to the estimation of the size of the infected pool in Australia to allow rational decisions regarding control of TB in Australia, including the possibility of introducing Mantoux screening and preventive therapy programs for high-risk groups.