Since there are no large-scale surveys of how cancer patients perceive unproven therapy in Japan, we wanted to clarify this issue by means of a cross-sectional questionnaire conducted among cancer patients. The survey revealed that 32% of cancer patients used unproven therapy without having sufficient information about it. There was a lack of communication between cancer patients and their physicians on topics relating to alternative medicine. Issues that we have to solve are concerned with the education of cancer patients, lay people and physicians on the meaning and role of alternative medicine and on the necessity for scientific evaluation of medical treatments in Japan.