Do You Need A Passport?

I will be going to Mexico soon for revision surgery and I am wondering if I have to have a passport to return to the U.S. Can my drivers license be used instead? 

drivers license and certified birth certificate

I was told by my surgeon in Mexico that they now require passports to get back into the US.

I have not been into Mexico for some time.  I was thinking about having some other procedures done in Mexico some time ago, and saw on one doctors website that you don't need one to pass into Mexico, BUT you will need one to get back into the U.S.  So, even though there will be transportation provided to cross the border, and transportation back into the U.S., I just don't want to risk any problems.  I have my passport ready.  

Yes, you do. I called the US State Dept. and asked because I was getting different answers from all over. Because of 911, unless you are on a ship, you will need to have a passport to re-enter the US.