Background: Many cancer patients use complementary and alternative medicine (CAM). Most websites offering online information on CAM are not helpful for them. Methods: We extracted decisive elements for online information on CAM by analyzing the literature on the information needs of cancer patients and on counseling cancer patients on CAM. Results: Key issues for online information on CAM are the qualification of the authors, transparency and accountability of the information, description of the aims, a scientific approach, description of treatment alternatives, support for the patient-physician relationship, individualized information, a summary of the information, disclosure of funding, and the privacy policy. Conclusions: The communicative challenge will be to convey information without destroying hope and motivation. We suggest that CAM topics should be integrated into broader information provided on cancer (etiology, conventional treatment). By also providing information for physicians, such a website could promote shared decision-making. Online information will gain the status of independent expert knowledge if provided by a well-known scientific organization as, e.g., a national cancer society.