While these are optional coverages in most states, it's a good idea to buy them. Here's why. If you are injured as a result of an accident caused by a driver who does not have insurance, Uninsured Motorists (UM) coverage will pay for your medical and hospital bills and other related expenses. If you have health insurance, some of these expenses may be covered, but you would still be responsible for deductibles and co-payments. And, of course, if you have no health insurance coverage or have selected a high deductible plan (also called catastrophic health insurance), you will be responsible for all or most of your expenses.Underinsured Motorists (UIM) Coverage works the same way. If you are injured by a driver who has insurance, but your injuries are greater than the amount of insurance they purchased, your own policy will pay your unpaid medical bills up to the amount of UIM coverage you chose to purchase (minus the amount the other driver's insurance pays).In some states, there is also a coverage called Uninsured Motorists Property Damage (UMPD) coverage. This coverage pays for your car if it's damaged by an uninsured driver and you have not purchased Collision coverage for your own car.