I ordered the medium and I am a full 36" waist.  Very comfortable.  They stay dry.  The waist band is comfortable and sturdy.  With some other underwear my waist band will roll over, but not with this one.  They are snug fitting which is what I like.  They could be little longer in the leg length, but acceptable.  I will be purchasing more of them.  I have tried many different branks.  UnderArmour works well also, but they tend to get hot and sweaty.  This one fits similarly, but is cool and comfortable.
Update Feb 2013.  I wear these much less due to the short leg length.  My new favorites are Target brand C9 by Champion.  They are a little longer in the leg, don't ride up and breathe well.  On sale for a 2pk around $12