This suit is wonderful for water aerobics on a chilly morning or sunny afternoon.  It is very light weight and easy to exercise in.  It dries very quickly.

Based on the sizing chart I ordered the extra small.  The bottom half fit perfectly but although I thought I carried most of my weight on the lower half, it was the top half of this suit that was tight as a corset.  Even if you only weigh a 100 lbs, I recommend that you get the small, rather than the extra small, if you have any bust at all and are not a tween.  Since the suit felt good overall, I am going to try the small now and will repost after I have tried it.

This suit is perfect for the snorkeling trip we take to Hawaii each year.  It keeps me warm enough that I can stay in the water as long as I want, and also means I'm not killing the coral with sunscreen.

Great product, witll shop at Swim Oulet again

I bought it for the wrong purpose.  I wanted to use it for warmth which it does provide, but not enough for swimming longer distances.  It gets real cold as soon as you get out of the water.  .  . probably very good for other purposes that people have mentioned (under a wet suit, etc)  I bought the small and may have needed an extra small. I am 5' 6" and weigh 120. It seems to fit well, but the arms can be pulled down to the middle of my hand, and the legs can be pulled about 3 inches from my heel, so perhaps I am carrying too much extra material with this size.

I still have, and love this suit.      I use it for swimming in a lake near my house. I have had it for a few months now, and I wear it twice a week.
I guess you really don't need to wear anything under it if you don't want to.    
I am really tall and have broad shoulders, so I is a pain to get off, or back on when wet.
It seems to be a bit short for my torso- but for the value it's pretty good!!