Introduction: Complementary and alternative medicine (CAM) is often used by cancer patients, yet, communication with the oncologist is poor. The objective of our study was to gather information on patients' usage of CAM, source of information, and aims, in order to derive strategies to improve the communication between physicians and patients on this topic. Materials and Methods: An online survey was conducted by linking a standardized questionnaire to the largest internet portal for cancer patients in Germany. The questionnaire addresses CAM usage, disclosure to physicians, source of information, objectives for using CAM, and perceived reasons for cancer. Results: Of 170 participants, 77% were currently using CAM. Disclosure to a physician was rather high with 63% having informed their oncologist. Asked whether the oncologist took time to discuss CAM, 74% answered ‘no'. Most frequently used are biologically based therapies, relaxation techniques, prayer, and meditation. Most patients want to reduce side effects, boost their immune system, and get active. Almost half the participants had positive experiences with some type of CAM before they fell ill. Conclusion: Understanding patients' concepts of the etiology of cancer and accepting their goals for using CAM may help oncologists communicate with their patients and guide them to a safe use of CAM.