300th episode makes 'Grey's Anatomy' one of the longest-running primetime U.S. TV series

The 300th episode of "Grey's Anatomy" screens November 9 on ABC. (© 017 American Broadcasting Companies, Inc. All rights reserved.)

When the 300th episode of "Grey's Anatomy" -- titled "Who Lives, Who Dies, Who Tells Your Story" -- screens Thursday, Nov. 9 in the U.S., the show will join the ranks of "The Simpsons," "Law & Order: Special Victims Unit" and "NCIS" as the only primetime series still on air to have reached this milestone.

Thursday evening, ABC will broadcast the seventh episode from season 14 of its hospital drama, which also happens to be the 300th episode of the series since it launched in 2005. To mark this special occasion, the show's creator, Shonda Rhimes, is celebrating the show's characters as well as paying homage to ghosts from the past.

The episode sees Meredith Grey and Alex Karev cross paths with victims of an accident at a county fair who look exactly like their former friends and colleagues George O'Malley, Cristina Yang and Izzie Stevens. This special episode also promises plenty of nods to the show's early days, when the main characters were still interns.

One of the longest-running primetime shows

"Who Lives, Who Dies, Who Tells Your Story" makes "Grey's Anatomy" one of U.S. TV's longest-running primetimes series still on the air. The current record holder is "The Simpsons," which saw its 623rd episode screen Nov. 5 on Fox. "Law & Order: Special Victims Unit" reached its 416th case Nov. 8 on NBC, and "NCIS" dropped its 337th episode Nov. 7 on CBS.

Some other shows are fast approaching the 300-episode mark. Animated series "Family Guy" screened its 294th episode on Fox Nov. 5. "South Park" has notched up 284 episodes, closely followed by "Criminal Minds" with 283 episodes. Plus, "Supernatural" and "The Big Bang Theory" total 269 and 238 episodes respectively since their launch.

Very few primetime series -- excluding soap operas, which can exceed 10,000 episodes -- have enjoyed such longevity in the history of U.S. TV. The all-time record is held by "Gunsmoke," with 635 episodes of the Western broadcast between 1955 and 1975. "Lassie" brought 591 stories to the small screen between 1954 and 1973, while "Bonanza" enjoyed 431 installments in 14 years on the air, and there were 380 episodes of "My Three Sons" during its 12-year run.

More recently, CBS axed its flagship series "CSI: Crime Scene Investigation" after 337 episodes, and NBC shut down "ER" after 331 episodes. Still, these impressive performances don't quite match the 1980s big-hitters "Dallas" and its spinoff "Knots Landing" with 357 and 344 episodes apiece.