In England the National Curriculum does not specifically mention the excretory system at key stages 1 and 2. Research by Reiss and Tunnicliffe (2001, 2002) has shown that children's knowledge of the organs and organ systems in their bodies increases with age but remains incomplete, even at maturity, unless they specialise in studying biology. The children were simply asked to draw what they thought was inside their body and were given no cues. All but the very young drew their own outline of the body and then inserted the organs and organ systems they could recall. In this article, the author investigates young children's understandings of the excretory and digestive systems. Children in years 3 (age 7/8) and 5 (age 9/10) were presented with two scenarios by their class teacher, while the author observed. The results suggest that even year 5 children lack understanding of the structure of the excretory system, although they have better understanding of the digestive system; they know that it is a continuous tube from mouth to anus. Discussion and implications for teaching are presented. (Contains 3 tables and 4 figures.)