(MONEY Magazine) – The Supreme Court's recent first-ever decision in a right-to-die case makes the most convincing argument yet for writing a living will. That's the document stating the circumstances under which you'd want doctors to withhold or withdraw life-sustaining treatments. In its late-June ruling, the court said that the state of Missouri could keep comatose Nancy Cruzan, 32, injured in a 1983 automobile accident, alive because her family hadn't shown by ''clear and convincing evidence'' that she would have wanted treatment terminated. Says Doron Weber, a spokesman for Concern for Dying/Society for the Right to Die, a nonprofit advocacy group: ''The court's decision underscores the importance of living wills because a written declaration should meet the clear and convincing evidence standard.'' In early July, 41 states and the District of Columbia had already passed laws specifying the terms under which living wills are considered valid. In the other nine states (Massachusetts, Michigan, Nebraska, New Jersey, New York, Ohio, Pennsylvania, Rhode Island and South Dakota), a court might need to decide whether a living will you have signed is enforceable. You needn't hire a lawyer to draw up a living will. Just get a preprinted form drafted to meet your state's living-will standards by writing to Concern for Dying/Society for the Right to Die (250 W. 57th St., New York, N.Y. 10107). The group also has general forms for the states without living-will laws. All forms are free, but a donation is requested. A living will should be signed, dated and witnessed by two people who won't become your heirs. If you want your lawyer to review the document, expect to pay $50 to $150. Keep the living will in a home filing cabinet or some other place that's readily accessible to your loved ones, not in a locked safe-deposit box. Give copies to your immediate family, a close friend and your doctor. You might also want to sign what's known as a durable power of attorney, a document naming a relative or friend to make decisions for you should you become incapacitated. Stationery stores sell fill-in power-of-attorney forms for about $1.50. Most legal scholars believe that durable power of attorney forms will cover health-care decisions. For more details about these subjects, write to AARP Fulfillment (1909 K St. N.W., Washington, D.C. 20049) and ask for the two free booklets Health Care Powers of Attorney (D-13895) and Tomorrow's Choices (D-13479).