This 5-year study demonstrated a statistically significant correlation between morbidity among children attending day-care centres and various weather parameters. The study was undertaken in south-central Sweden, where sharp seasonal contrasts in climatic and weather conditions occur. Illness-associated absence (IAA) decreased significantly when the weather was bright, sunny and warm, determined using average monthly weather parameters analysed over 60 months. This may be because good weather encourages outdoor activities which, in turn, reduce the risk of spreading respiratory tract infections as outdoor play areas are larger, body contact is less frequent, and any bacteria and viruses present will be readily dispersed. In multiple regression analysis, outdoor temperature was the most prominent parameter linked with IAA. This may reflect the behaviour of the staff with regard to various weather conditions. It is therefore to be recommended that children attending day-care centres should be allowed and encouraged to play outdoors when conditions allow. (C) 2004 The Royal Institute of Public Health. Published by Elsevier Ltd. All rights reserved.