Objective: The purpose of this study was to identify determinants of comprehension of an educational pamphlet on colon cancer, by adults at least 50 years of age living in the United States. Design: Data were analysed from the "2003 National Assessment of Adult Literacy" survey. The survey was designed to assess functional English literacy, which included reading a colon cancer pamphlet, among American adults. Setting: The survey was carried out at interviewees' homes. Method: Data from 1231 adults who were 50 years of age or older were selected for the current study (mean age = 63.22 years). Results: Multiple regression analysis revealed that comprehension difficulties increased with age ([beta] = -0.13, p less than 0.001). Non-Black minority adults had poorer comprehension than Whites ([beta] = -0.10, p less than 0.001). Adults with a high school or further education had better comprehension than those with lower-level education ([beta] = 0.22, p less than 0.001). Comprehension was higher among adults who often received health information by talking to their health providers ([beta] = -0.12, p less than 0.001), and for adults who had high levels of verbal-reading fluency ([beta] = 0.24, p less than 0.001). In addition, increased English reading habits alone only marginally contributed to comprehension of the pamphlet ([beta] = -0.06, p = 0.06). Conclusion: Understanding the pamphlet was related to age, ethnic background, education, reading fluency and experiences in communication with health providers. Increasing communication between health providers and patients or tailoring the written materials to improve adults' knowledge of colon cancer is recommended. (Contains 4 tables.)