Understanding the problem of health literacy is crucial when writing for patients. It is the single best predictor of an individual’s health status, stronger than age, income, employment status, educational level, and racial or ethnic group.2–3 Although it is not always clear who is not health literate, health literacy is increasingly vital to help people navigate a complex health system and better manage their own health. Differences in the ability to read and understand materials related to personal health as well as navigate the health system appear to contribute to health disparities. People with low health literacy are more likely to report poor health, have an incomplete understanding of their health problems and treatment, and be at greater risk of hospitalization.4The average annual health-care costs of persons with very low literacy (reading at grade two levels or below) may be four times greater than for the general population.5An estimated 75% of persons in the United States with chronic physical or mental health problems are in the limited literacy category.6People with chronic conditions, such as asthma, hypertension, and diabetes, and low reading skills have been found to have less knowledge of their conditions than people with higher reading skills.7One study8 at a women’s health clinic found that, among patients considered to have low literacy, physicians identified only 20%. This emphasizes the need for awareness of this condition by physicians.