I wear a small, i am 5ft 5.5in, 138lb, a medium fits better around the waist,  but had to go with the small, because of the length, everything is really long, just like you see on the picture, but you want it for work because the shirt really, really doesn't ride up. Before I discovered this shirt i wore other brands and kept puling the shirt down throughout the day, very annoying. I never have to worry about this problem anymore:)
I experimented with the medium, which is wider, but also longer,  but I had to hem it about an inch, so I can wear it out with the leggings. Small is perfect for work under the scrub top, thanks, Cherokee!