The tag says "Shadowline" and says "Petite." I would gage it as a modern day size small.
This reminds me of something June Cleaver or Betty Draper would wear to bed. The best part is that it is very comfortable and slinky so you will sleep well and look beautiful. The best part is that this set appears to never have even been worn - there is no wear, pilling, stains, holes, etc.
This set would make a great shower present for a bride to be.
Here are the measurements:
Bust: 18" (one side, armpit to armpit)
Waist and Hips: free
Length: 32" (back neckline to hem)
Bust: 20" (armpit to armpit, one side)
Sleeve: 14.25" (shoulder seam to cuff)
Shoulders: 15" (across the back, seam to seam)