In this qualitative study, four nurses of a teaching hospital in the city of Campinas, São Paulo-Brazil, all of them working with oncological patients were interviewed in order to verify the situation that most caused mental suffering in the day by day with these patients. Data collection were performed as proposed by the ethnographic approach and the non-directive interview and the direct observation was employed. The contain analysis has been utilized to the data analysis. The results have shown that many situations of the relationship nurses-oncological patients cause mental suffering in that professional. Those situations are tied to the work of the nurses, to the kind of patient treated by those professionals and to the kind of sickness presented by the patient. That study has shown that, many times, the nurses utilize defense mechanisms against that mental suffering. This work aims to contribute to the knowledge of the subject and therefore be itself a base in which one could elaborate measures that can make these problems that occur with the nurses that work in the Oncology area lighter. With that study to contribute to the comprehension of the challenge that the cancer, sickness that make professional and population frightened, is.51273-90