1.
Preston Burke
Burke and Cristina were just about to be married, but instead, Burke left Cristina at the alter at the end of Season 3. He returned in Season 10 briefly, offering Cristina a job in Zurich.
2.
Addison Montgomery
Addison also left in Season 3, heading to Calfornia. She didn't leave us entirely, though, since we were able to enjoy her character more fully on the spin-off, Private Practice.
3.
George O'Malley
The first doctor to be killed off and cause us to cry ugly tears, George was hit by a bus while trying to save another person. His friends all tried to save him, not realizing who he was until he finally was able to communicate his identify by tracing the numbers "007" on Meredith's hand.
4.
Izzie Stevens
Izzie overcame cancer and was even re-hired after being fired from the hospital, only to decide to leave Alex and everything else behind.
5.
Erica Hahn
Erica Hahn just sort of disappeared, last seen heading to her car never to return to the hospital.
6.
Lexie Grey
Causing even more ugly crying, Lexie Grey was a victim of the plane crash in Season 8. It was completely devestating.
7.
Mark Sloan
It almost seemed like Mark had a chance. He made it out of the plane crash alive, but was in a coma for months. He woke up long enough to give us a few more smiles and final words before he died.
8.
Teddy Altman
Teddy was fired by Owen in Season 8 so she would take a job she was offered by the U.S. Army.
9.
Cristina Yang
At least Cristina was written off without being killed. She left at the end of Season 9, taking over as head of Burke's hospital in Zurich -- an opportunity that was perfect for her character.
10.
Derek Shepherd
The most shocking and emotional exit of them all, Derek Shepherd left in Season 11, killed in a car wreck after saving the lives of several others. He didn't die instantly, but was instead taking to a hospital where the doctors made a series of mistakes in trying to save him.