After reading the remarks on sizing, I had to decide how tight I wanted this item to fit...I am 5'4 125, small shoulders, skinny arms, large in the chest (D)...I ordered a large... It fits tight... but is not uncomfortably tight around the neck or underarms... This item is thicker than my other rash guard and twice as expensive..but it is well made and looks great in solid black.....I could have worn an X large but am happy with this fit as I have a loser fitting rash guard as well...I felt the top was a tiny bit to long.. It covers the top of my bikini bottoms as I am short waisted......You have to decide how you want it to fit on your body..Skin tight (with comfort in neck and arm area) or a tiny bit of room?  ...Good luck... PS if you have a belly it will show...