The Difference Between Uninsured and Underinsured Motorist Protection
Uninsured motorist protection provides a benefit in case you're involved in an accident with someone who is "at fault" but has no insurance.
Underinsured motorist protection provides a benefit if you're involved in an accident with an "at fault" driver who has some insurance, but not enough to fully compensate you for your injuries. I suggest you get out your policy take a look see what limits of liability you have. The limits for uninsured and underinsured motorist coverage should be equal to the limits you carry for Bodily Injury liability.