Quote Pemps="Pemps"My Wigan Kooga one is large. My NZ All Golds (ISC) is medium. I have a couple of 'classic' shirts and they're medium. I'm a 42" chest.'"
Depends how fat you are.
I'm a medium in Classic and ISC but I recently bought a Medium NZ Warriors Canterbury jersey and it was tiny! If you're a medium in the UK go for Small or Medium in NRL, or better still go to the match and try one on!