The National Child Development Study (NCDS) is a birth cohort study whose longitudinal design makes it suitable for examining the natural history of common diseases in childhood such as atopic eczema. We have analysed the age of onset and clearance rates for examined and/or reported eczema in 6877 children born during the period 3-9 March 1958 for whom linked data were available at birth and at the ages of 7, 11, 16 and 23 years. Of the 870 cases with examined or reported eczema by the age of 16 years, 66% had age of onset by the age of 7 years. Of the 571 children with reported or examined eczema by the age of 7 years, the proportion of children who were clear in terms of examined eczema or reported eczema in the last year at ages 11 and 16 years was 65% and 74%, respectively. These 'apparent' or short-term clearance rates fell to 53% and 65%, respectively, after allowance for subsequent recurrences in adolescence and early adulthood. Age of onset of community-ascertained cases of atopic eczema may be later than that reported in hospital-based studies. The long-term prognosis of childhood eczema may be worse than some previous studies have suggested, especially when subsequent recurrences are taken into account.