I went by the sizing chart and according to the chart, I'm a small.  According to the measurements, I'm in between the small and medium.  I typically wear a small size 4 with sleeveless.  Other reviews said the material had some stretch, so I gave it a shot.
I'm 5'4, 136 lbs with a 36" D chest 27" waist in jeans.  I'm very lean and athletic build.  I could barely get the top buttoned.  I want to reorder, but I don't even think the medium would fit up top and would make the pant area way too big as the pants on the small fit perfectly.  The fabric is really nice and the color blue is beautiful.