I am 5'3", 135ish lbs, petite but athletic build, 32C. I can usually wear an extra-small in dresses that are not super fitted but since this was strapless (fitted around the bust), I ordered a small. I was almost in tears when I couldn't get the zipper up... the small was WAY too small. Once my disappointment and vanity wore off, I ordered a medium and I am thrilled to report it fits amazingly. besides being too long, of course, everything else fits great and is very flattering. so besides running small, in my opinion, dress seems to be beautifully constructed.