The long-running medical drama will bow out in February 2009 after 15 years on the air. The last season will run to 19 episodes.
"ER is one of the greatest shows of all time and we can't wait to deliver to the audience the fantastic stories the series is known for," said Ben Silverman, co-chairman of NBC Entertainment. "We will introduce new characters to the great ensemble."
As well as new characters, producers are rumoured to be courting former stars to return for the final episodes.