Aim: The aim of this study is to determine the nutritional habits of cancer patients based on the diagnosis types, the changes in the food frequency before and after the diagnosis, and to determine the purposes and types of nutritional supplements used by the cancer patients and by whom the supplements were recommended. Metods: Totaly 116 patients, 55 from medical oncology and 66 from radiation oncology were included in the study. Questionnaire about general knowledge, nutritional habits, pre and post diagnostic food frequencies was performed by face to face interview. SPSS for Windows 15.0 program has been used for the statistical analysis of the study findings, p<0.05 was accepted as the degree of significance. Results: When the findings were evaluated; it was found that 28.4% of the patients were using supplements, they mostly started to use with the advise of doctor (75.8%), and 75.0% of them were using the supplements to support of their treatment. It was determined that the use of supplement was not related with age, gender, cancer types and the most commonly used supplement was omega 3. The patients consuming supplements were found to use frying as a cooking method statistically lower than the non-use patients (p<0.05). It was found that 2.6% of patients consulted with dietitian. When pre and post diagnostic food frequencies were evaluated, no statistical differences was found between the two (p<0.05). Conclusion: The use of dietary supplements is generally directed by doctors. It has been observed that likelihood to make healtier choices after the diagnosis is not as expected to be. Even though benefit is showed in the literature, dietary consulting of the patients and their belief about the benefit of nutrition on the treatment of disease is found to be low. Ongologic branching out of dietitian may lead to the increase of the awareness among patients about affect of nutrition on threapy.