Kevin Clash, 53, has lent his voice to the furry red monster Elmo on the pre-school program for more than 20 years. He also voiced the character of Baby Sinclair on Jim Henson's prehistoric puppet show "Dinosaurs."
Sesame Workshop said Monday a 23-year-old man contacted the show's producers in June and alleged he had a relationship beginning when he was 16 with Clash, who has denied he did anything improper.
"We took the allegation very seriously and took immediate action," Sesame Workshop said in a statement.
"We met with the accuser twice and had repeated communications with him. We met with Kevin, who denied the accusation. We also conducted a thorough investigation and found the allegation of underage conduct to be unsubstantiated," the statement said. "Although this was a personal relationship unrelated to the workplace, our investigation did reveal that Kevin exercised poor judgment and violated company policy regarding Internet usage and he was disciplined. Kevin insists that the allegation of underage conduct is false and defamatory and he is taking actions to protect his reputation. We have granted him a leave of absence to do so.
"Elmo is bigger than any one person and will continue to be an integral part of 'Sesame Street' to engage, educate and inspire children around the world, as it has for 40 years."