The present study examined children's understanding of illness in a peri-urban community in South Africa where AIDS is prevalent (n=138). Results suggest that children were surprisingly knowledgeable about AIDS at an early age, and may have even erroneously analogized from AIDS to the flu. Furthermore, all age groups attributed different causes for AIDS (transmitted by blood) and flu (casual contagion). However, although factual knowledge about AIDS was identified among all age groups, there was no evidence of understanding biological causal mechanisms. The data have implications both for developmental research on biological reasoning in diverse cultural contexts and for the design of health education programs.