The other reviews are accurate in saying that these pants are snug. However, they worked perfectly for me for what I was using them for. I wore these pants basically 72 hours straight when climbing Mt. Shasta in July. I had no problem wearing the Patagonia Capilene Lightweight bottom underneath. I liked the snug fit of the pants because it kept them from getting in the way while mountaineering. They were unbelievably breathable, fantastic at moisture wicking (we were in snow for 2/3 days), and overall worked really great for what I was using them for. Dirt came off easily, which I had not expected to appreciate, but when you have one pair of pants for 3 days that kind of detail starts to matter. I even wore them glissading (sledding on snow without a sled) for about 4k vertical feet, and although my butt got painfully cold, I was actually shocked that the pants took the insane friction without the smallest indication of the strain. Even better, they were completely dry within 20 minutes.
I am usually size 4, and although the pants were tighter than I was expecting, they ended up being the ideal fit for what I needed them for. If you are bulkier in the thighs, butt, or stomach, or if you just want a roomier fit, I would recommend going at least one size up.
Overall, I am beyond satisfied with these pants, and I'm excited to put them to more use in the future.