Grey's Anatomy has been on the air since March 27, 2005, and is easily a household franchise, well-known across the world. More original cast members have left the show in the last few years, than ever before. Currently the only "OG Intern" is Ellen Pompeo, who plays Meredith Grey.
If you wanna get real technical, Chandra Wilson, the woman that plays Miranda Bailey, is also an original cast member. As of right now, James Pickens Jr., the actor behind Richard Webber, is still on the show. However, the question fans are asking now is... for how long?