My boyfriend is an avid surfer and I got this to replace his worn out rash guard. I was hesitant to buy this online as some reviewers mentioned the top didn't run true to size, but he's 5'10" 170lbs with a 43" chest, normally wears a medium or large in tshirts and the Large fit him perfectly, a bit snug but not too much or too little. Great material and well made, I'm very impressed.