I ordered a size M because of the other reviews saying that runs really small. The M fits me fine ( I'm 5'6" and 112 lb) but I think I could have ordered the SM. It is a bit hard to put it on, but not harder that putting on a sports bra! Same thing when I took it off. A little hard, but not bad at all. The bra area fits a little strange on me. While the dress fits nicely everywhere, under my arms feels a little too big. I am a A/B cup and its a little big there too. But because I bought to wear under an itchy dress, it really doesn't matter bcs it won't show.
Overall, it's a great product. The material is very nice and comfortable. I ordered the black checker and it looks great.