I'm 5'6", 140 lbs and usually wear a 6/8 or a medium.  Couldn't decide based on the comments so bought both a medium and a large.  Large was too big and had a small hole in the front.  Medium was an OK fit, but it's a thin knit fabric and shows every bump.  Navy was true to color, skirt was comfortable and a good length.  One could wear with a slip or spanx underneath to form a better shape, but I sent them both back.