I ordered 17, 36/37. My standard shirt size is 16-16.5, 36/37 but for slim fit, 17 works best for me. I am 6'1", 255lbs. I find that IZOD generally fits comfortably for bigger guys (like myself).--==Update==--Dropped from 5 star to star (I didn't go 1 start because I like the shirt colours, just hate it's ironability (new word)So, after 1 wash, I will never buy this Stretch material Izod shirt again. THEY ARE IMPOSSIBLE TO IRON!I even had to do some research into the material blend to see if that was the cause but I also but some other brand shirts with the same composition and they are not so difficult to iron. I iron 25 shirts in a single sitting every 6 to 7 weeks. One of these shirts takes me 30 minutes to get to some semblance of acceptability but not really ironed well. The first time I iron 2 and stopped. I said this is ridiculous. The lines would not budge. I gave up and decided that for the first time in my working life, i'll have my shirts ironed by the dry cleaner. I've uploaded some pics of a shirt done by the dry cleaner and you will see, even they had problems because the final product was not a crisp as I am used to.I will be looking for another type of shirt for my next purchase. Hopefully Izod does away with this stretch material failure.Note: I bought 7 different colours/styles of this shirt - they are all the same in difficulty to iron. The darker colours show up the lines more than others.