If the show had been brought back for another season it would have surpassed "Gunsmoke" as the longest-running TV drama series in U.S. history. Right now, the two shows are tied for that distinction.
NBC said Friday it has ordered a 12th season of the spinoff "Law & Order: Special Victims Unit," as well as the new series "Law & Order: Los Angeles" for the 2010-11 television season.
The original "L&O" is to end its 20-season run May 24, the network said.
The announcements were made Friday by Angela Bromstad, president of prime time entertainment for NBC and Universal Media Studios.
"'Law & Order' has been one of the most successful franchises in the history of television, which is why it is so critical that we continue this important brand and our relationship with Dick Wolf and his team with 'LOLA' and 'Law & Order: SVU,'" Bromstad said in a statement.
"The full measure of the collective contributions made by Dick Wolf and his 'Law & Order' franchise over the last two decades to the success of NBC and Universal Media Studios cannot be overstated," said Jeff Gaspin, chairman of the NBC Universal Television Entertainment. "The legacy of his original 'Law & Order' series will continue to make an impact like no other series before."