ObejectiveTo test the hypothesis that children attending child care centres are more likely to be prone to acute respiratory illness.DesignA case‐control study.SettingA community‐based study in the Adelaide metropolitan area.ParticipantsA randomly selected sample of Adelaide children whose births were registered in 1983.Main outcome measureA respiratory illness score was calculated for each child, based on parents’ reports of acute respiratory illness in the previous 12 months.ResultsInformation was obtained by postal survey for 2618 children (mean age at time of study, 26 months). Eight hundred and nineteen of these children (31%) were reported to be regular or occasional attenders of child care centres or creches. Home interviews were carried out with parents of children whose respiratory illness scores fell in the top 20% of the range and those whose score was in the bottom 20%. Children prone to respiratory illness were more likely to be users of child care centres or creches than the children who were not prone (odds ratio = 2.28; 95% confidence interval, 1.53–3.40). The risk of being prone to respiratory illness increased with the frequency of use of child care, and tended to be greater the younger children were when they first attended child care centres. Adjustment in multivariate analysis for confounding factors made little difference to the strength of the association of proneness to respiratory illness with the use of child care (adjusted odds ratio = 2.23; 95% confidence interval 1.38–3.61).ConclusionUse Of child care centres is an important cause of acute respiratory illness among Australian children.