Purpose: Do-not-resuscitate (DNR) decision-making in severely ill patients presents many difficult medical, ethical, and legal challenges. The primary aim of this study was to explore cancer patients’ and health care professionals’ attitudes regarding DNR decision-making authority and timing of the decision. Methods: This study was a questionnaire survey among Danish cancer patients and their attending physicians and nurses in an oncology outpatient setting. Potential differences between patients’, physicians’, and nurses’ answers to the questionnaire were analyzed using Fisher’s exact test. Results: Responses from 904 patients, 59 physicians, and 160 nurses were analyzed. The majority in all three groups agreed that DNR decisions should be made in collaboration between physician and patient. However, one-third of the patients answered that the patient alone should make the decision regarding DNR, which contrasts with the physicians’ and nurses’ attitudes, 0% and 6% pointing to the patient as sole decision-maker, respectively. In case of disagreement between patient and physician, a majority of both patients (66%) and physicians (86%) suggested themselves as the ultimate decision-maker. Additionally, 43% of patients but only 19% of physicians preferred the DNR discussion being brought up early in the course of the disease. Conclusions: With regard to the decisional role of patient vs. physician and the timing of the DNR discussion, we found a substantial discrepancy between the attitudes of cancer patients and physicians. This discrepancy calls for a greater awareness and discussion of this sensitive topic among both health care professionals and the public.