Kevin Clash, the longtime voice and puppeteer behind “Sesame Street’s” Elmo character, resigned on Tuesday after a new allegation was made that he had underage sexual relationships.

Announcing the decision with what he called a “very heavy heart,” Mr. Clash said in a statement, “Personal matters have diverted attention away from the important work ‘Sesame Street’ is doing and I cannot allow it to go on any longer. I am deeply sorry to be leaving and am looking forward to resolving these personal matters privately.”

His statement came at around the same time that a lawsuit was filed in federal court in New York accusing him of “sexual activity” with a 15-year-old. The accuser, Cecil Singleton, is now 24. The suit said that Mr. Singleton “did not become aware that he had suffered adverse psychological and emotional effects from Kevin Clash’s sexual acts and conduct until 2012.” It sought $5 million in damages.

Mr. Clash had no comment on the lawsuit. He was first accused last week of sexual improprieties by a man who later recanted and said they had an “adult consensual relationship.” That man has remained anonymous and has not filed a suit.

While Mr. Clash’s departure on Tuesday put some distance between the sex allegations and the iconic children’s character, the claims may affect the “Sesame Street” brand in ways that remain to be seen.

Hasbro, the main toy licensee for “Sesame Street” products, said in a statement Tuesday, “We are confident that Elmo will remain an integral part of ‘Sesame Street’ and that ‘Sesame Street’ toys will continue to delight children for years to come.” Macy’s, in a statement, said the episode would have no bearing on “Sesame Street’s” presence in the Macy’s Thanksgiving Day Parade later in the week.

Jim Silver, editor in chief of Time to Play, a Web site that follows the toy and licensing business, estimated Hasbro’s wholesale sales of “Sesame Street” branded toys to be about $75 million annually. Elmo-related products account for 50 to 75 percent of that figure, he said, depending on the year.

Before Mr. Clash resigned, Mr. Silver said he was estimating that Elmo-related toy sales would be down perhaps 10 percent because of the stories about Mr. Clash’s personal life. But with the resignation, he said, the total impact will probably be less than that. This fall, Hasbro’s Playskool brand introduced “Playskool Sesame Street LOL Elmo,” a new version of 1996’s “Tickle Me Elmo,” with a suggested $40 retail price tag.

“People are making the separation that this is about Kevin Clash, this is not about Elmo,” he said. “The more people make the separation, the less effect on sales.”

Mr. Clash took a leave of absence last week to defend himself when the first accuser received attention from the gossip Web site TMZ. Production of “Sesame Street” will be unaffected by his absence, in part because Mr. Clash had been helping to identify other puppeteers who could play Elmo.

Still, his name has been synonymous with Elmo for more than 20 years, and especially so since his star turn in a documentary, “Being Elmo: A Puppeteer’s Journey,” last year. The complaints this month contributed to what Sesame Workshop, the producer of “Sesame Street,” on Tuesday called a distraction.

“None of us, especially Kevin, want anything to divert our attention from our focus on serving as a leading educational organization,” the organization said in a statement. “Unfortunately, the controversy surrounding Kevin’s personal life has become a distraction that none of us want, and he has concluded that he can no longer be effective in his job and has resigned from ‘Sesame Street.’”

The statement concluded, “This is a sad day for ‘Sesame Street.’ ” The organization declined interview requests.

After the resignation announcement, there were unanswered questions about whether Mr. Clash was forced out by the organization (whose publicists announced his departure an hour before his own personal publicist did).

Katherine Franke, a professor of law and the director of the center for gender and sexuality law at Columbia University, said she worried that Mr. Clash was “the most recent victim of what we call in my world a ‘sex panic.’ ” She named a second recent example, David Petraeus, who admitted having an extramarital affair and resigned as the C.I.A. director earlier this month.

“At precisely the moment when gay people’s right to marry seems to be reaching a positive tipping point, sexuality is being driven back into the closet as something shameful and incompatible with honor (in the case of Petraeus) or decency (as in the case of Clash),” Ms. Franke said in an e-mail message. Mr. Clash, she added, “has not been convicted of a crime, but merely accused of one in a completely unsubstantiated, vague complaint.”