These are great slippers for warmth, but they do run small.  I wear a ladies 8 and found that the medium is too small.  I wear them as mules because I can't get my foot all the way in comfortably and didn't want to go to the trouble of returning them.  There is also zero padding on the bottom, so they're ok on carpet but not at all supportive on tile or wood floors.  I probably won't buy them again.