Introduction: Recently published articles have established that a substantial number of cancer patients utilize the Internet to gather information about their respective diagnoses. The challenges for medical providers include understanding the prevalence and characteristics of patients using the Internet, reasons for Internet use, and the effectiveness of currently available websites in providing useful health-related information to patients. Material and methods: Adults with cancer were asked to complete a self-administered, anonymous, 21-item questionnaire upon registration at the Alvin J. Siteman Cancer Center at the Washington University School of Medicine. Results: There were 500 respondents (mean age 58 years (range 18-90), 83% Caucasian and 15% African-American). Three hundred ninety-eight participants (80%) reported access to the Internet, and 315 (63%) reported searching for information about cancer on the Internet. Patients accessing the Internet for cancer information were younger than those who did not (median age 56 vs. 63 years; p<0.001). Internet usage for cancer information also differed by race (p<0.0001) and education (p<0.0001). Among patients who searched the Internet for cancer information, 13.3% of patients had their decisions towards treatments affected or changed, and 11.4% of patients had their choice in physicians affected or changed because of Internet use; 23.5% of patients sought information on clinical trials, and 9.5% of patients were influenced or changed their decision regarding clinical trial enrollment due to Internet information. Discussion: Approximately two thirds of patients with cancer used the Internet to obtain information about their disease. Factors affecting Internet use for cancer information included age, race, and education. Clinical decisions can be affected by Internet use.