I'm 5'11, 145 lbs, normally size 8 or 10. I got the medium, which is supposed to fit up to a size 12; totally doesn't. It's on the short side, the front slit is really big, and the darts for the dust were almost under my armpits.  However, the material is thick enough to sew, so I ripped the shoulder seams and used cross-stitched ribbon along the shoulders to add length. I sewed up the big front slit, using extra dress material I trimmed from the back side of the chest seam. The little attachment in front is just cheap stretchy ribbon, easy to cut out.  Least see-through of all the Morticia costumes I've seen. With the modifications I made, it looks more appropriately gothic, not quite as long as her floor-length gown in the movie, but has a waist and shape to it, so even though it's now sewn up to where the little elastic band was, still looks hot. Gomez approved.