This shirt is a welcome addition to my tiki shirt rotation. Have receive multiple compliments. My suit size is 37S and I ordered the XS based on measurements. I fits like a glove - so much so that I'm a little afraid to wash it for fear of shrinkage. I generally like my clothes a bit more fitted so this works for me. If you are the same size as me and prefer a looser fit, I'd say go with the S.