Since the dawn of time, humans use plants to relieve their ills and diseases; cancer is no exception to this rule. Traditional medicine is an important part of health care but often underestimated. Aim of the study: The purpose of this investigation was to determine the prevalence of Medicinal Plants use in oncology, establish the list of plants used to treat cancer and evaluate this practice risks on the health of patients. Methods: Cross-sectional study based on a questionnaire on the use of medicinal plants by patients with cancer in unit of oncology of the university teaching hospital IBN Rochd of Casablanca, Morocco. A questionnaire was distributed to 1325 patients in face to face interviews. Results: Our study involved 1325 patients. Women made up 75% of the population, compared with 25% of men, with a ratio of 0.33. The found prevalence of plants use in our population of patients was high at 38%. 63 herbal medicine species under 38 families have been identified. The most commonly used species were essentially the Marrubium vulgare L followed by the Aristolochia longa, the Berberis vulgaris. Seeds, leaves and fruits are the most commonly used plant parts of plants to treat cancer. Decoction and infusion were the most commonly used method of preparation. The most common type of cancer treated with traditional medicines was breast cancer followed by uterus, colon and leukaemia. Conclusion: This survey provides an updated list of medicinal plants used by the entire Moroccan population. To assess the efficacy and the safety of reported herbs, Clinical and randomized trials are needed hereafter.