Use of complementary and alternative medicine (CAM) is very frequent in cancer patients. The aims of this study were to analyze the frequency, the reasons of use of CAM in patients with a cancer treated in a Moroccan oncology department. We included in this study 400 patients. An anonymous questionnaire was proposed to patients during treatment. Over 384 analyzable questionnaires, 71% of patients were using CAM. The most frequent method was religious therapy (60%). The second one was herbal medicine (36%). The main reason for using CAM was reducing psychic pain in 53%, and boosting the immune system in 32%. Adverse effects were reported in 2% of cases. Only 5% of patients discussed CAM with their doctors. The cost of CAM was less than 100 Euros in 88% of cases. To optimize the patient-physician relationship and to avoid a propensity to unproved treatments, accurate and adequate communication is necessary.