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."