Several reviewers stated that the item runs small, so I bought a size larger...I was absolutely swimming in it.  I have to return for a smaller size.  The costume itself is really nice, though.

Update--so I returned the Large and ordered a Medium.  As I said, the Large was literally falling off of my shoulders it was so big, but when I got the Medium, it was so little I couldn't even get my arms up into the cosume to try it on!  I looked at the tag, thinking that they must have made a mistake, but sure enough, it was a medium--a very, very small medium.  I am really disappointed because as I said, the costume is really cute.  It is going back, because I absolutely cannot wear it.