Healthy children, children with seizure disorders, and children with orthopedic conditions, ranging in age from 5 to 16 years old, were questioned about their knowledge of disease etiology, treatment, and prevention, and their health locus of control beliefs, to explore the relationship between illness-related concept attainment and perceived control over health. Children who perceived greater personal control over health demonstrated a more sophisticated conceptual understanding of disease than did children with a more external orientation. Healthy children scored significantly higher on the illness concepts questions and expressed significantly more internal health locus of control beliefs than did their peers with a chronic physical illness. Perceived control over health appears to be one factor that mediates the relationship between illness experience and understanding.