Eileen married David Lampson in 1968, they later divorced in 1975. The marriage produced two sons: Patrick Oliver in 1973 and Samuel John in 1974. Shortly after her career took off, Brennan was injured in a near-fatal automobile accident. As a result she had to fight a long battle to overcome dependency on prescription painkillers. She triumphed and was back on-screen in the mid-1980s.