Previous research has indicated that treatment staff often underestimate the informational needs of cancer patients. In this study, the authors determined the total number of information sources obtained and used to influence treatment decisions, and the clinical and demographic factors associated with the use of specific sources of information in cancer patients. Participants were identified by the statewide cancer registry and diagnosed in 2004 with breast, colorectal, lung, or prostate cancer. A self-administered mailed questionnaire elicited cancer treatments, demographics, and information sources used to make treatment decisions. Of those surveyed, 1,784 (66%) participated and responded to all questions regarding information use. Over 69% of study participants reported obtaining information from a source other than the treatment staff. Significant predictors of using additional information sources included younger age, higher income, higher education, complementary and alternative medicine (CAM) use, and reporting shared decision making (all p values <.01). Participants with a college degree were more likely to use the Internet (OR 3.7; 95% CI 1.5-9.0) and scientific research reports (OR 3.3; 95% CI 1.6-6.9) to influence treatment decisions compared with those without a high school degree. Support group use to influence treatment decisions was not associated with socioeconomic variables but did vary by cancer type and CAM use. The sources of information study participants obtained and used to influence treatment decisions varied strongly by socioeconomic and demographic variables. These findings provide a deeper understanding of the information needs of cancer patients and have implications for dissemination strategies that can minimize disparities in access to cancer information.