When you're married, who pays for medical bills may not be much of an issue -- you'll work it out between you. Whether you're legally liable for each other's medical debts is a far more complicated issue. It comes down to state law and the rules can differ considerably from one jurisdiction to the next.
Community Property States
If you live in one of the community property states -- California, Arizona, Texas, Nevada, Washington, Wisconsin, Louisiana, Idaho and New Mexico -- the "marital community" is responsible for all debts incurred during your marriage. The marital community is you and your spouse jointly.
Equitable Distribution States
Although community property states are relatively consistent in their laws, the other states -- called equitable distribution states -- are anything but. In some states, you're never contractually responsible for medical bills incurred by your spouse unless you sign something guaranteeing payment on her behalf. In others, health care expenses that benefit either of you are considered marital debts if they're incurred during the marriage, so you're both responsible. How necessary the medical care is can also make a difference. If your spouse is unable to pay for required care but you can afford it, you might be responsible. This is the case in states that hold that spouses have a legal responsibility to provide each other with necessities. If you don't live in a community property state, check with a local lawyer to determine the rules where you live.