Decisions about withdrawing and withholding treatment are common in health care. During almost every encounter between health professionals and patients a decision needs to be made about treatment options. In most cases these choices do not pose any difficulty, for example, starting antibiotics when a patient has an infection. However, decisions not to treat, or to stop treating, raise fundamental questions about the nature and purpose of nursing and the ethics of end-of-life care. This article argues that nurses need to be proactive in deciding what is nursing care and what is treatment. An ethical distinction is drawn between acts and omissions. How this distinction relates to withdrawing and withholding treatment will be considered. Further ethical issues discussed relate to judgements about the futility of treatment, patient autonomy and nurses' duty of care to patients at the end of life.