They fit a wee bit tighter then I'd like. I'm a size 9-10 in pants and bought a Medium (which is usually what I order universally). A slight 'muffin' effect happens where the shorts end on my thigh (actually more above the knee because I'm short), which isn't very desirable, but I don't really mind it. They are perfect for lots of movement and running without your shorts flapping in the wind (and without chafing if you do wear something over it).
I also love the length.