My 38 runs true to size. It's quite fitted though, so if you think you may be looking to layer beneath it then you might want to consider going up one size...that said, the narrow sleeves probably mean you couldn't wear anything much thicker than a chambray shirt or a fine polo neck (those are what I wear under it) anyway.CBI said:true to size - at least for me, I had one and one of the few regrets of jackets I have sold!