Competency in health numeracy is essential in understanding risk about disease susceptibility and the consequences of disease treatment. Both health literacy and skill in using the Internet to obtain health information are lower among older compared with younger adults. Presentation format of health information has been shown to influence comprehension. The objective of this study was to determine the influence of information formatting (text and graphic) on older adults' comprehension of Internet-based numeric cancer risk information. This cross-sectional study involved a convenience sample of adults, aged 50 years and older from diverse ethnic and educational backgrounds. Cancer risk information, obtained from a Canadian Cancer Society web page, was presented as text, graphics or as a combination of text and graphics formats. Comprehension of the information was assessed by six questions focused on basic numeracy skill and ability to perform simple calculations and operations. A three-item general context numeracy and an eight-item health context numeracy instrument were used to describe health numeracy skills of participants. The six-item Newest Vital Sign (NVS) test was used to assess prose and numeric health literacy. There was no statistically significant effect of presentation format on participants' comprehension of the cancer information. Participants' comprehension of basic health numeracy information was positively correlated with education (p < or = 0.05) and income (p < or = 0.01) whereas comprehension of information that assessed calculation and operations numeracy skill was positively correlated only with income (p < or = 0.05). Health literacy skill and income explained a significant proportion of the variance in overall comprehension of Internet-based cancer risk information (R(2) = 0.414, p < or = 0.01) in this sample of older adults. Format of numeric risk information was not a significant factor in the comprehension of cancer risk information in this group of ethnically diverse, older adults. However, comprehension of the information was related to health literacy skill and income.