The AAMC has instituted new procedures for dealing with multiple acceptances and committing to a particular school, so be sure to read communication from individual medical schools carefully. When you receive your first acceptance in writing, look at your list of medical schools and withdraw from those lower on your preferred list that you know you would not attend over the school where you've been accepted. It is a courtesy to other candidates and to the medical schools themselves to cancel scheduled interviews at schools you know you would not choose over the one where you've been accepted. When you receive two acceptances, choose between the two and withdraw from the one you like less. An exception to this procedure is if you are waiting to see what financial aid you will receive, or if you are gathering information to help make your decision. It is customary for schools to return your deposit if you withdraw before April 30th.
If you are genuinely struggling to decide between 2-3 schools it is OK to hold multiple acceptances while you visit the schools and gather more information. You MUST decide at least 21 days before orientation begins at the school you will attend.
As of April 30, you should not hold more than one acceptance. However, you may remain on wait lists of other schools until you begin orientation at the school where you've committed to attend. If you withdraw from a school after April 30, you will lose your deposit at that school. See the AAMC's Recommendations for Medical School Applicants (http://www.aamc.org/students/applying/recommendations/applications/).