I purchased the Medium originally, but they were so big and sloppy looking that I decided to purchase the Small too. The small turns out to be a true small (size 4-6), but I'd say that the Medium is more like a size 10-12. I guess I need a size 8! For reference I'm 5'7 and 130lbs. My waist is disproportionately small for my rear, so I usually have to size up which make the waist too big. The mediums were just big all over.