This costume was awful - I turned right around and returned it.  I am 5'4", size 10, and ordered this in a Large.  The top was a bit snug (I usually wear a medium top) but the bottom was so big and extremly unflattering.  The skirt made my hips look like it was a foot rounder than it really is.  Had I known how to sew, I would have thought about keeping it and making some alterations but I'm not that domestic (unfortunately).