An increasing number of breast cancer patients are accessing the Internet for medical information. A survey was administered to breast cancer patients and their families attending follow-up outpatient clinics in a comprehensive cancer care center to explore their frequency of Internet use, their motivation for online activity, the type of information they sought, and the perceived impact of the information they found on the Internet on their medical care. The survey was conducted over a 4-month period. A total of 107 surveys were returned. Seventy-nine of these (74%) were from patients while 28 (26%) were from family members and friends. Thirty-four of the patient responses (43%) indicated that the patient had used the Internet to look for cancer-related information. Patients who had used the Internet to access cancer-related information were significantly younger (P = 0.007), better educated (P = 0.027), and less satisfied with the amount of treatment-related information given by caregivers than those patients who had not used the Internet to access cancer-related information (P = 0.032). The majority of patient Internet users desired more information on their cancer and its treatment (91%), looked up information that was presented to them by their clinicians (66%), researched other treatment options (63%), and obtained more information on "alternative treatments" (63%). Patient Internet users generally found the cancer-related information on the Internet to be useful, and the majority discussed Internet-derived information with their health care providers and perceived that clinicians listened to such information. However, 53% were undecided about the trustworthiness of the medical information obtained via the Internet. Internet nonusers commonly lacked Internet access (53%) or were unfamiliar with the Internet (33%), but few (13%) distrusted Internet-derived information. This exploratory study underscores the need for more research in this area, specifically with the aims of identifying and verifying factors that lead patients to use the Internet and the impact of their online activities on their medical care.