text: Registered Nurse here; First let me clear up the myth, (untruth about mononucleosis), it does not stay with you for life.  The incubation period is about 7 to 21 days, give or take 3 or 4 days in either direction.  Someone that had mono 6 years ago, is in no way, shape, form or fashion caring it today, unless they have been re-exposed to the viral infection.