Patients followed up with a cancer diagnosis must be well-informed about cancer to be able to cope with it. Besides, informing the relatives of the cancer patients who are also experiencing the same process about the diagnosis and follow-up period of cancer is highly important. In the current study, it was aimed to evaluate the information sources about cancer which are referred to by relatives of cancer patients. Three hundred ninety-one cancer patient relatives were included in medical oncology clinic between May 1 and June 30, 2015. A questionnaire was applied to the participants, comprising 12 questions to elicit demographic information and 11 questions about the information sources to which they referred. The study included 183 female and 208 male participants with amean age of 47.9 +/- 13.6 years. While the oncologists were the primary information sources referred to by 87%, the Internet was the second most preferred information source by 72%. The websites most frequently referred were the official websites (70%), the websites of oncology associations (53%), and social networks and forums (32%). The primary factors affecting the Internet preference were age, education level, income level, and place of residence. The Internet was the second most referred information source about cancer by family caregivers following oncologists. Therefore, it is of crucial importance that physicians inform patients and their relatives comprehensively as well as guiding them to correct and reliable information sources.