I wear a size 6/8 & ordered the Medium, they fit great and are soooo super cozy.  The only complaint I have is that the drawstring does not have the means to stay outside the little holes on the waistband, so despite tying knots on the ends, the string has been sucked inside the waistband area a number of times & I've just given up on it.  After a wash, the fabric is holding up pretty well & the microfleece did not get fuzzy or rough.  I may be going back in for a 2nd pair of these for winter!