The purpose of this study was to examine the effect of changing key factors in survey questions on public opinion regarding end-of-life decisions. These factors were: (a) patient prognosis (likely vs unlikely to recover from the illness); (b) end-of-life practice (foregoing treatment vs assisted suicide vs euthanasia); and (c) and decision making process (competent patient vs incompetent patient based on living will vs incompetent patient based on family wishes). A representative quota sample of 2019 Canadians 18 years of age or older were surveyed using a 13-item questionnaire with 12 items eliciting attitudes towards end-of-life decisions. The questions were systematically varied according to three key factors; patient prognosis, end-of-life practice and decision making process. One item assessed whether respondents had completed a living will. In the case of a decision to forgo life-sustaining treatment in a competent patient, public approval was 85% if the person was unlikely to recover and 35% if the person was likely to recover. In the case of a competent patient unlikely to recover, public approval was 85% for forgoing life-sustaining treatment, 58% for assisted suicide, and 66% for euthanasia. In the case of forgoing life-sustaining treatment for a patient unlikely to recover, public approval was 85% for a competent patient, 88% for an incompetent patient who had expressed his/her wishes in advance through a living will, and 76% for an incompetent patient based on a family's request. The influence of these key factors was similar in other cases examined. Ten percent of Canadians said they had completed a living will. It was concluded that patient prognosis has a major effect, end-of-life practice a moderate effect, and decision making process a minor effect on public opinion regarding end-of-life decisions.