Not sure if it truly runs small as i didn't have an xs to compare with, but i picked up the s at the store and that fit really nicely. had a loose flow about without it looking big on me. i'm 5'0, 32 d 110lbs and have a petite but athletic build. and i normally wear xs. the sleeves were a snug fit, not in an uncomfortable way because the material is stretchy but i would wonder if an xs would have been too tight around the arms, and the chest not creating that flows look. very feminine, sweet and