This study examined the understanding of 5- and 9-yearsld children about health and four illnesses, using open-ended, probed interviews. Younger children were more Likely to centre on their current state of health as being completely healthy or ill, while older children could envisage a stare of partial health; less centring was found in judgements of future health for both ages. Older children were more aware of strategies for preventing heart attack and broken arms, though not for preventing chickenpox. The majority of both younger and older children gave strategies for avoiding colds as well as for staying healthy. Older children had greater awareness of objective and non-observable. physiological signs of some illnesses, as well as of objective symptoms. Few children mentioned non-observable symptoms of any illness. The coding scheme used in classifying children's responses about illness provided detailed information about children's knowledge of specific illnesses, and showed that young children have considerable knowledge about health and illness issues. Results were interpreted in term of children's changing access to knowledge about health issues rather than solely by reference to cognitive develop mental stager.