I bought a Medium because my measurements were in the low end (bottom end) of that category on the size chart. The cup size fits good (I'm a 32C) but the band size is definitely too big. My boobs are falling out. I'm having it altered so it fits me tighter. If I bought it again I'd buy a small, even though I was closer to the medium size.
Other than that, this top is so sexy and hot. I love it!