On the eve of his departure from ABC’s “Nightline” after more than 25 years, Ted Koppel has a parting shot for the advertising community.

“Madison Avenue and the advertising industry it represents are under the illusion that it is more important to get 22-year-olds than it is to get 50-year-olds [to watch],” Mr. Koppel said in a recent telephone interview with TelevisionWeek. “That has never made a lick of sense to me, because my experience has been that I had a helluva lot more money when I was 50 than I did when I was 22, and I buy a lot more stuff. I would think the advertisers would love to get my attention and draw me to their products, but for some reason they think that you’ve got to get them young and that that is the important thing to do, and as long as they believe it, it is so.”

When Mr. Koppel and senior executive producer Tom Bettag take their leave of ABC on Nov. 22, it will be the end of “Nightline” as we’ve known it for more than 25 years. Cynics are betting that a revamped “Nightline” with Cynthia McFadden, Martin Bashir and Terry Moran as rotating anchors and contributors will last only as long as it takes ABC Entertainment to develop a more lucrative program to play at 11:30 weeknights.

Mr. Koppel attributed his departure at this particular time to “a combination of factors. One is I’ve been doing it for a very long time. It is clear to me there is a lot of pressure to bring in a younger audience if they can do it, most particularly younger women, and while I have no problem at all with putting on programs that should be appealing to women-I mean, we’ve tried to do that many times over the years-I’m old-fashioned. I grew up when news divisions didn’t make money and we weren’t supposed to be responsive in any way to that kind of economic pressure.

“It wasn’t that [ABC and Disney] did it that surprised me. That kind of thing doesn’t surprise me anymore. I just didn’t much care for the way they did it,” said Mr. Koppel, who understands that TV programming was created to induce people to watch commercials.

Even today, ABC-affiliated TV stations that reach nearly 11 percent of U.S. TV homes pre-empt “Nightline” to run syndicated programming from which they reap all of the commercial revenue.

“So with that as context, I fully understand that The Disney Co. at one point felt it would be wise to bring David Letterman over here and that they could make more money at 11:30 at night with David on than they could with ‘Nightline’ on,” he said, referring to a well-publicized 2002 incident in which he was blindsided by the news that ABC had offered CBS talk show host Mr. Letterman the “Nightline” time slot. The strategy backfired in large part because Mr. Letterman, an admirer of Mr. Koppel, did not want to be responsible for the newsman losing his groundbreaking spot in ABC’s lineup.

Mr. Koppel said he and Mr. Bettag intend to continue their long collaboration, adding that word of their first post-ABC News projects is likely to come soon after they officially separate from the network. Mr. Koppel joined ABC in 1963 at age 23, and Mr. Bettag joined in 1991 after a strong partnership with former “CBS Evening News” anchor Dan Rather.

“We’re kind of old-fashioned news people, and we still think there are a lot of serious issues that need to be covered. Just where we’re going to find a forum or a platform is less important than that we still do them,” Mr. Koppel said. There’s no word on talks that were said to have taken place with HBO, one of the last bastions of long-form nonfiction TV programming.

Looking back, Mr. Koppel said he is proud of having “maintained our standards from Year 1 through Year 26. In this day and age, that is no small achievement.”

Over three decades his interviews ranged from presidents-elect to Miss Piggy. He would be lampooned-inspiring generations of “Saturday Night Live” mimics and comparisons to Mad magazine’s Alfred E. Neuman-almost as respectfully as he and “Nightline” would be honored by their peers. He moderated international TV peace summits and national town hall meetings and covered more than one war.

Mr. Koppel laughed when he recalled how he and former executive producer Leroy Sievers trained with 10-mile runs and 40-pound backpacks for the rigors of covering the war in Iraq, only to be embedded with a thoroughly mechanized Marine unit when they arrived. “We didn’t have to walk anywhere. We didn’t have to carry anything. We had our own vehicles,” Mr. Koppel said.

His run on “Nightline” was not without its controversy: In April 2004, Mr. Koppel and Mr. Sievers’ decision to read the list of Iraq war military casualties on the air made headlines when the Sinclair Broadcast Group accused “Nightline” of making an antiwar statement and refused to carry that night’s program.

Only Johnny Carson lasted longer in late-night TV than Mr. Koppel, who made his imprint on the nation’s consciousness during the Iranian hostage crisis beginning in late 1979 with ABC News’ “America Held Hostage.” The 11:30 nightly telecast evolved into “Nightline” in March 1980.

According to Nielsen Media Research data, “Nightline” is up 2 percent season to date in the news demographic of 25- to 54-year-old viewers and is off only 1 percent in total viewers.

As to the future of the program without him, Mr. Koppel said, “I think you do news programs based purely on what is important out there and what you think, in your best judgment, is going to have the greatest impact. Anytime you start looking at a program and saying, ‘Should we try to tweak what we do based on whom we’re trying to appeal to?,’ I think that’s a step in the wrong direction.

“Now, I don’t know that’s where ‘Nightline’ is going to go. I truly don’t. But if they move in that direction, that would the wrong way to go.”