Many seniors — perhaps even a majority of Americans older than 65 — don’t have a living will, also called an advance directive.

“The ramifications of not having one are so severe that it’s bewildering that more people don’t do it,” says Howard Krooks, past president of the National Academy of Elder Law Attorneys. Without that document, which spells out your health-care wishes if you are unable to speak for yourself, your loved ones will have to guess. If they disagree, the problem could end up in court. (You can download state-specific forms at www.caringinfo.org.)

Important as these documents are for older people, young adults should also put their wishes in writing. Only 7 percent of those ages 18 to 29 have an advance directive. But at age 18, a person is an adult for purposes of medical decision-making. Before leaving for college, he or she should sign a Health Insurance Portability and Accountability Act release form and a health-care proxy giving someone — typically, a parent — the right to review personal medical information and to make decisions in an emergency. Otherwise, the young person’s loved ones may be locked out of information and decisions.

Your proxy is the person you designate to make health-care decisions for you if you can’t. Not having a proxy is like not having a will: Without it, your decisions will be made by the default person specified in your state’s law. That is especially critical for same-sex married couples in states that don’t recognize their union. Needless to say, it’s important that your proxy understands your wishes and agrees with them. Make sure you update your proxy on any changes in your documents.

“If you have a medical crisis and somebody calls 911, EMTs will come to your house and be on you quickly,” says California geriatric-care manager Linda Fodrini-Johnson. “They won’t read through a long advance directive.” If your health has deteriorated to the point where you don’t want resuscitation, have your doctor sign a do-not-resuscitate (DNR) order. Keep it where it can be easily found by EMTs — perhaps hanging it near your front door in a clear plastic sleeve.

An advance directive isn’t always enough. Those who are so ill or frail that they might die within a year may benefit from a POLST form. Short for “Physician Orders for Life-Sustaining Treatment,” it is much more detailed than a DNR. For instance, in a POLST you can specify whether you want to be tube-fed indefinitely, on a trial basis or not at all. (POLST is not available in every state. To learn more, go to www.polst.org.)

Your family and your health-care proxy need copies, and they should have easy access to duplicates of other key documents. If you are in fragile health, it’s wise to “have a hospital-ready packet close to your front door,” Fodrini-Johnson advises. In addition to documents, the packet should have the names and contact numbers of family members and doctors, your medication list and your POLST form (if you have one). Two free ways for family members to electronically share such documents are by using the My Health Care Wishes app (for Android and Apple) and by visiting the MyDirectives Web site (www.mydirectives.com).

Must-ask questions

After Boston Globe columnist Ellen Goodman was overwhelmed by end-of-life medical decisions for her mother, she co-founded the Conversation Project (www.theconversationproject.org). To start talking about your concerns, it suggests such questions as:

Do you want to live as long as possible no matter what, or is quality of life more important than quantity?

Would you accept nursing-home care? Or is independent living a priority for you?

Do you want to know just the basics about your condition, or as much as you can?

Do you want your doctors to do what they think is best, or do you want to have a say in every decision?

Are there any disagreements or family tensions that you’re concerned about?

Are there circumstances you’d consider worse than death, such as not being able to recognize family?

Copyright 2015. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.