So I am a bit confused by some of the reviews on sizing here.  I am 5'5 and a size 6 and the S/M fit PERFECTLY!  The M/L would be HUGE on me!  I think if you around a size 4-8 buy the S/M, not the M/L.  They are leggings so they should fit snugly.  I do see what others said about hte back being lower than the front, that is odd but does not pose much problem as my butt isn't very big.  But overall, great leggings!!!