Im a 36D and got a medium.  I don't want to take it off!!!  Its so comfortable that I sleep, wake up and get going in the morning with it on.  Love this bra.  There is no uni-boob and no falling out at the bottom. Im delighted.  I must say I like the material of coly/poly, less concern about drying.  Im ordering more.  Id like one with lace, but cant have everything especially because I love the racerbacks.