It is often the case in dietary assessment that it is not practicable to weigh individual intakes of foods eaten. The aim of the work described was to estimate typical food portion weights for children of different ages. Using the data available from the British National Diet and Nutrition Surveys of children aged 1 1/2-4 1/2 years (1992-1993) and young people aged 4-18 years (1997), descriptive statistics were obtained, and predicted weights were calculated by linear, quadratic and exponential regression for each age group. Following comparison of energy and nutrient intakes calculated from actual (from an earlier weighed intake study) and estimated portion weights, the final list of typical portion sizes was based on median portion weights for the 1-3- and 4-6-year age groups, and age-adjusted means using linear regression for the 7-10-, 11-14- and 15-18-year age groups. The number of foods recorded by fifty or more children was 133 for each of the younger age groups (1-3 and 4-6 years) and seventy-five for each of the older age groups. The food portion weights covered all food groups. All portion sizes increased with age with the exception of milk in tea or coffee. The present study draws on a unique source of weighed data on food portions of a large sample of children that is unlikely to be repeated and therefore provides the best possible estimates of children's food portion sizes in the UK.