I bought the small.  I am 5'5" 120 lbs, size 4.  They are very comfortable but snug.  I would probably buy Medium next time. That is why 4 stars vs 5.  I was worried they would be too long and wasn't sure I'd like the waist.  Not too long at all - perfect after several washings.  The waistband is probably my favorite thing.  It doesn't cut or squeeze you, so you don't get any annoying bumps or bulges.  Recommend!