I love these shirts, I have 4 of them now. I had bought 2 a few years ago and love them to travel, they are perfect for layering under dresses and blazers, or as a protective layer under wool sweaters, and work well as pajamas too. I think they run true to size as a 'fitted' turtleneck. I have them in both medium and large, the large tends to stretch out over the day and becomes a little baggy, the medium is more consistently fitted so is better for wearing under low cut dresses. They are a little see through, but if you wear a black bra it is fine and can be a little sexy if you want to wear it that way. The 2 I got a few years ago seem to be better quality than the ones I ordered here, the wrist seam opened on the medium one after 1 wash, and I wash them in delicate bags. But whatever I guess, I they are so soft and comfortable and very flattering. I also did not find the neck to be too tight on any of them as other reviews have suggested, but I wear a lot of turtlenecks so many I don't notice.