old check

What is the name of your state (only U.S. law)? Florida

A refund check was mailed to me in 1991, from the University of South Florida.
I had moved out of state just prior to the mailing. Now that I have the check(17 years later), is the University of South Florida under any obligation to re-issue a new check? or have I legally forfited the money?

After 17 years, you have no legal way to collect the money any longer. But if you present it to the school nicely, they might be so amazed that you held onto a check for 17 years that they voluntarily re-issue it. (Don't hold your breath though).