Questionnaires on CAM were sent to 2118 clinical oncologists in Japan. The questionnaires gathered data on background (age, gender, years in practice, specialty and knowledge of cancer CAM), perception (effectiveness/ineffectiveness, scientific evidence and drug interactions) and attitude (experience with, and response to, CAM users). Questions about oncologists’ perceptions and attitudes to CAM were limited to herbs and other natural products that were sold over the counter. A total of 166 questionnaires were returned as undeliverable. Of the remaining questionnaires, 751 were returned (a response rate of 39%). The majority of oncologists (82%) believed that CAM products were ineffective against cancer. The main reason for this belief was a lack of reliable information (as cited by 85% of oncologists). Only 13% of oncologists had experienced CAM-associated disease improvement in their cancer patients. Of all the oncologists, 84% considered the possibility of drug interactions between anticancer drugs and CAM products. The majority of oncologists (80%) replied that they could neither promote the use of CAM products nor recommend quitting the products, when they were asked about the use of CAM products by cancer patients.