Through the magic of technology, I can tell what people are searching for on the Internet when they find my website. One of my visitors googled "do I need a health care proxy if I am married?" I'm not quite sure why the person thought they might not need one just because they were married, and the answer is a resounding YES!
A health care proxy is a vital document for everyone over 18. This document allows you to appoint someone you trust to make health care decisions for you in the event of your incapacity. For instance - if you are in a car accident and are unconscious for a few hours or days, or you have a stroke and are incapacitated for a longer time.
You need this document even if you are married. You can, of course, appoint your spouse as your health care proxy, but you should also appoint an alternate in case you and your spouse are both incapacitated.
Without a health care proxy, your doctors will turn to your family to make your decisions, probably your spouse first. But, if your parents and spouse disagree about your care, this can cause real problems (see Terry Shiavo). The best thing to do is execute a health care proxy appointing the person you choose as your health care agent and then talking to that person and your other family members about your wishes.
You can download a Health Care Proxy form (for Massachusetts) here, or if you are getting ready to visit your attorney to do your other estate planning, she can prepare a health care proxy for you along with your other documents, usually at no extra charge.