I ordered this rash tee to use while on a week long beach vacation.  It's certainly a nice product.  Although I wear a Medium in a cotton t-shirt, and I ordered a medium Honolua rash shirt, I'd go with a small next time.. mostly because I would have liked a slightly more "fitted" feel.  It most likely is true to the size of a Medium shirt, but if you're going to be in the water, it helps if the shirt fits a bit closer, though still not tight.  I did end up replacing it with a rash shirt from a local surf shop on vacation in a size Small and found that much more to my liking.

I would still reccommend this product, I'd just get a different size for myself next time.

Remember when shopping rash guards and shirts, that a standard fitted rash guard will be cut to have a "compression" type fit (tight).  If you want something more like a t-shirt to wear in the water, get a rash "tee" shirt, but consider a size smaller than you normally might wear.  Four stars instead of five since a boardshort connector might be nice to have if you want it (small loop on the front of the shirt you can lace your boardshorts through to keep em together).