Runs a little large, the butt was kind of baggy in the padding area. I'm a healthy size 12, with a muffin top, and I bought a large...I feel that a medium probably would've fit, but the large is usable. Outside of the butt, the rest of the shorts fit very comfortably, not too tight, comfortable elastic...I really like them, and would recommend them.
Great liner and, with the pattern, these could be worn alone in a pinch if your shirt was longer. They aren't see through and obviously liners as some others that I have. Love that the pad is wider than most in the back, I have a lot of "seat" to cover.