I purchased a medium, I am 5'6 and 135 (usually a 38B or 36C) and this was too small for me, unfortunately it isn't adjustable around the back so I couldn't do anything to loosen it.  Also the design on the back really accentuates if you have any back fat!  So I have to return it.  The cup size was ok for me but it didn't really do a lot to push anything up.  If you are less than a 36 around under the bust then this would probably be ok for you.