Graduated from Oak Park River Forest High School.
Italian-American.
Listed as one of twelve "Promising New Actors of 1986" in John Willis' Screen World, Vol. 38.
Of all the people ever to be nominated for an Academy Award for acting, Mastrantonio has the longest name.
Once trained for a career as an opera singer.
Replaced Robin Wright, due to pregnancy, as Maid Marion in Robin Hood: Prince of Thieves (1991) with Kevin Costner.
Sons Jack O'Connor (born 1992) and Declan O'Connor (born 1997) with Pat O'Connor.
Suffered a serious mental and emotional breakdown during the problem-plagued shoot of the James Cameron film The Abyss (1989).
Was neighbors with Alan Rickman in London in the early 90's. They worked together in January Man and Robin Hood Prince of Thieves.
Was nominated for Broadway's 2003 Tony Award as Best Actress (Musical) for portraying the Aldonza/Dulcinea character in a revival of "Man of La Mancha."