The present study explored concepts of illness held by children with intellectual disability (ID) and compared them with the beliefs of two comparison groups of typically developing children who were matched for cognitive developmental level and chronological age (ns = 11). Content of responses to questions regarding illness causation, symptoms, treatment, and prevention was analyzed; children with ID provided significantly different responses than did children without ID. A positive association between cognitive development and prevention concepts was found for children with ID. Children with ID did not differ from developmentally matched children in sophistication of illness concepts. Thus, it appears important to assess cognitive developmental level of children with ID to provide appropriate health education and services.