Effectively designing risk information for the public is challenging and selecting the appropriate medium to deliver disease risk information is crucial. In a usability evaluation of a colon cancer risk website, we evaluated the public's understanding and interpretation of graphical displays of risk information (2 bar graphs). Results from this study suggest that many people do not understand risk and often misinterpret graphical displays of risk and associated terminology. This work shows the importance of not only including representational analysis within user-centered design of consumer health websites, but also evaluating the health and numerical literacy levels of these websites as an aspect of usability testing.