Background: Many cancer patients are interested in complementary and integrative medicine during and after regular cancer treatment. Given the high number of users it is important that physicians and patients engage in a dialog about useful complementary and integrative medicine therapies during cancer treatment. In a prospective, multi-center, cluster-randomized evaluation study we will develop, implement and evaluate a training program for oncology physicians advising their patients on complementary and integrative medicine. The main objective of the study is to evaluate whether training physicians in a blended-learning approach (e-learning + skills-training workshop) in providing advice to their cancer patients on complementary and integrative medicine, in addition to handing out an information leaflet about reputable websites, has different effects on the outcomes of patients, physicians, and their interaction level, compared to only giving out the information leaflet. Methods/Design: Forty-eight oncology physicians will be included into a cluster-randomized trial to either participate or not in the blended-learning training. Physicians will then advise 10 cancer patients each, resulting in 480 patients participating in the trial. The blended learning consists of nine units of up to 45 min of e-learning and 18 units of up to 45 min of on-site skills-training workshop focusing. Outcomes will be measured on the physician, patient, and physician-patient-interaction level. Discussion: A blended-learning program for oncology physicians to advise their cancer patients in a systematic way and a reasonable time frame on complementary and integrative medicine will be evaluated in depth in a large cluster-randomized trial.