The BBC is investigating up to 10 "serious allegations" involving past and present employees, director general George Entwistle said.
He gave the figure as he faced a hostile grilling from MPs about the broadcaster's handling of claims of sexual abuse by former presenter Jimmy Savile over several decades.
He told the Commons Culture, Media and Sport Select Committee, when pressed on the scale of current internal investigations: "We are looking at between five and 10 serious allegations relating to activities over the whole period in question, the Savile period."
That included claims of sexual harassment made against people still working at the BBC, he added, but he could not say how many.
Mr Entwistle said Savile's alleged behaviour had been possible only because of a "broader cultural problem" at the BBC. And there was insufficient evidence yet to say whether or not abuse was "endemic". But he said it was important to differentiate between complaints of sexual harassment and those of criminal behaviour, such as under-age sex.
Opening the hearing, the director general defended the Corporation's handling of the case - including setting up two independent investigations.
"I would accept that there have been times when we have taken longer to do things than in a perfect world I would have liked," he said. "But I think if you looked at what we have achieved since the scale of the crisis became clear, I think you see we have done much of what we should have done and done it in the right order and with proper respect paid to the right authorities."
Mr Entwistle said the inquiry by Nick Pollard, former head of Sky News, into why the Newsnight investigation into Savile was dropped is expected to report back "in weeks". He told the committee that he had ordered an internal audit of the operation of the BBC's child protection policies and would report its results to the BBC Trust in December.
Mr Entwistle was also facing criticism over the decision not to broadcast a Newsnight investigation including interviews with Savile's victims last year. His appearance before the committee came the morning after the BBC's Panorama programme broadcast an investigation into Savile and into the decision to ditch the Newsnight film, at a time when he was head of TV. Newsnight editor Peter Rippon stepped aside on Monday after the BBC said his explanation of why the show dropped its investigation into Savile was "inaccurate or incomplete".
The director general told MPs he believes the Newsnight investigation into Savile should have continued. "I came away from Panorama firmly of the view that that investigation, even if, in the judgment of the editor, it wasn't ready for transmission at the point he was looking at it, should have been allowed to continue." Mr Entwistle said there had been a "breakdown of communication" between Newsnight reports and the editor, Mr Rippon, and he did not feel "confident" he could get an explanation over what happened from within the BBC.