Patients with critical neurologic illness typically have impaired capacity to make their own medical decisions. In these cases, neurologists need to make medical decisions based on advance directives (such as a living will) or the decisions of a surrogate. A hypothetical case of a 60-year-old man with an intracerebral hemorrhage is used to highlight some of the difficulties that can occur when attempting to apply general statements made in a living will to a specific medical treatment decision. The ethical and legal issues surrounding surrogate decision making as they apply to acute critical neurologic disease are discussed, along with suggestions for how to resolve potential disagreements.