I am 5'3", 132lbs. and rather muscular, so I ordered Medium, which is my normal size, the first time. It was too loose-fitting around the waist for my liking and longer than expected. Someone else may prefer a looser fit, but I wanted more shape-forming.I ordered a Small and it is perfect! ...not tight, yet nicely hugs the waist and not too long either, just right!So, I'd have to say it actually runs a bit big in my usual size of Medium. I love it! The material is soft and a little stretchy, very comfy!