I'm 5'7", 125lbs and I ordered this in a small.  Fits perfectly HOWEVER - I can wear up to 6" heels with this no problem.  Makes you look like your legs are a mile long.  Haven't figured out what kind of bra to wear yet but that's ok.  The only reason I have 4 stars and not 5 is because the one I received was used.  It was repackaged, wadded up in plastic.  No tags or weird tissue paper...I'll run it through the delicate cycle and hang it dry..  I'll either have to always wear heels or have it tailored so I can wear flats with it.