Cameron Diaz misses her long hair .... big time!

While visiting The Tonight Show with Jay Leno, the What to Expect When You're Expecting star shared her regrets about her recent haircut.

The 39-year-old actress tells Leno:

    "There was a little misunderstanding. I said I just wanted a little bit cut off and it went from here to here. It was one of those moments where I just couldn't ... I just burst into tears."

We think she can pull off that short 'do! Cam adds, "I felt so vulnerable. For a woman to all of a sudden have no hair ... oh my God!"

Diaz turns 40 soon! Talk about sexy at any age.