The law recognises the right of a competent adult to make an advance refusal of life-sustaining medical treatment. This right is based on the principle of self-determination which dictates that a competent adult is entitled to make decisions about the kind of treatment he or she wants to receive or not to receive. However, the right to refuse life-sustaining treatment in advance is not unqualified. There are circumstances in which a health professional or a court will be entitled to disregard an advance directive and provide the life-sustaining medical treatment. This intervention is justified on the grounds of the State's interest in preserving life. Although self-determination prevails over the State's interest in life, the courts have held that an adult's wishes need only be respected if the adult has expressed them clearly and there is otherwise no uncertainty. This paper explores in some detail the common law and statutory excuses available to health professionals in Australia who do not wish to comply with directions in an advance directive to refuse life-sustaining medical treatment. At common law, the inquiry revolves around whether the adult intended his or her refusal to apply to the circumstances that have subsequently arisen. The paper considers the different situations in which it might be argued that an adult completed an advance directive but did not intend it to apply, thus permitting a health professional to disregard it. In contrast, the relevant Australian statutes specify a number of excuses that expressly allow a health professional not to follow an advance directive, or prohibit him or her from following it. The paper then compares the common law with those jurisdictions that have enacted legislation and critiques the different excuses available. The paper concludes by asserting that the law generally strikes the correct balance between requiring an advance directive to be followed but not enforcing a direction to refuse life-sustaining medical treatment where there is some doubt about whether it presents the adult's views. However, there are two riders to this proposition. The first is the tendency of the judiciary to err unduly in favour of the sanctity of life when it is called upon to interpret whether an advance directive can be regarded as representing the adult's wishes in the situation that subsequently arose. Secondly, comment is made about the recognition in one statutory jurisdiction of an excuse that permits a health professional to provide treatment contrary to an advance refusal based on good medical practice.