Objective: Medicinal herbs are commonly used as complementary or prophylaxis in common illness, as well as in diseases such as cancer, where the disease is severe. In order to determine the use of plants and mushrooms among cancer patients, a survey was conducted with 100 cancer patients who are receiving treatment at polyclinics at the Istanbul University Institute of Oncology. Material and Methods: The questionnaires were conducted face to face with the patients and the results were evaluated in computer. Results: According to the survey results, only 24 of 100 patients were found to use the plants and mushrooms for treatment, to reduce the side effects of the treatment or to feel better. As a result, it was determined that a total of 17 different plants and 1 mushroom were used. The mechanism of action, side effects, and warnings of these plants and mushrooms on cancer treatment have been investigated. With this study, it was determined how the patients obtained the plants and mushrooms, how the age, gender or socioeconomic status affect the plants and mushrooms used and what kind of feedback the patients give about their experience. Conclusion: The fact that the plants and mushrooms are not supplied by pharmacies, the application of herbal treatments with the advice of people under the title "expert" and "reliable" cause many problems. The survey study yielded promising results about the use of plants and mushrooms by cancer patients in Turkey. Similar studies are expected to be conducted in more clinics.