BACKGROUND: With the passage of the Patient Self-Determination Act in 1990, new procedures and documents became available for planning end-of-life care. These new procedures and documents are now being examined scientifically. OBJECTIVE: To review existing research on the use of advance directives. DATA SOURCES: Computer search using Grateful Med software from the National Library of Medicine with MEDLINE and BIOETHICSLINE databases. STUDY SELECTION: Studies that showed an emerging consensus or reported vastly differing results were selected. Selected studies examined these specific areas: demographic data on patients with advance directives, completion rates, capacity to complete, patients' preferences, stability of patients' decisions over time, treatment choices, proxy decision makers, treatment provided, and cost. RESULTS: The body of important research about advance directives is growing. A profile of their clinical utility is emerging. CONCLUSIONS: The research done so far can stimulate future research and can begin to suggest possible changes in practice. However, the body of research is not yet large enough or well controlled enough to answer conclusively many of the questions about planning of end-of-life care.