Call it a split decision in the late-night ratings wars last week.

CBS’ “Late Show With David Letterman” took the crown in the overall race, averaging 3.7 million viewers each night compared with 2.8 million for NBC’s “The Tonight Show With Conan O’Brien,” according to figures released Thursday by Nielsen Media Research.
But O’Brien, who took over the franchise from Jay Leno on June 1, was tops in the demographic that many advertisers consider most important, people between the ages of 18 and 49. NBC averaged 1.4 million viewers in that category, while CBS had 1.1 million.
NBC said the median age of O’Brien’s audience last week was 46.7, compared with 57.3 for Letterman.