it can be done, depending on the school. note however, that there is usually a lengthy process involved. there are a bunch of forms and agreements you sign, saying you'll take X amount of time off and still want them to reserve a seat for you. plus you need a really good reason (e.g. family/financial problems, year off for research, etc.), and most schools give you a max. of 1 year deferment. check with the schools.