i think it depends on what you want to do.... and certain schools insist that they don't allow it at all (BU), but if you had a good enough reason, it would be worth a shot anyway. what were you thinking of deferring for? the best idea would be to just call admissions offices of schools you're interested in and checking... also, do a search about deferring on SDN. there are threads from before (i think i posted a few.... i'm deferring a year 😉)...