I purchased this particular rash guard in red/black because I really liked the design and chose the XL after reading reviews that noted the sizing runs rather small.  I am absolutely delighted with both the design (looks even better in person) and fit, but here is where I confess that I am a busty female who wears a 12 in girl sizes.  I don't know how most men would fit into this thing, but I would recommend it for average-to-large females.