Nice looking shirt, EXTREMELY small. We ordered a Large. If you have absolutely no belly, and toothpicks for arms, this would be fine. My 51yo hubby has a little dad belly (not much though) and muscular arms (not body builder arms, but he does physical labor and has muscular arms). The body is snug, under the arms and the sleeves are so snug as to be extremely uncomfortable. He has given the shirt to our 25yo SIL who typically wears a size Small, and it fits him well, slightly roomy. I would recommend ordering a size larger if you are slight build and two sizes larger if you have slight chub or are muscular.