The London theatre that Kevin Spacey used to run says an investigation received 20 personal testimonies of alleged inappropriate behaviour by the actor.
Spacey served as artistic director of The Old Vic between 2004 and 2015.
In a statement, The Old Vic said an investigation by an external law firm had heard 20 allegations of incidents relating to The Old Vic ranging from 1995 to 2013 - with all but two taking place before 2009.
The review found that, in all but one case, the individuals alleging inappropriate behaviour did not come forward at the time.
None of those who raised the complaints were minors at the time of the alleged incidents, and the theatre stresses that it has been unable to verify the accounts.
However, the investigation is said to have found that "[Spacey's] stardom and status at The Old Vic may have prevented people, and in particular junior staff or young actors, from feeling that they could speak up or raise a hand for help."
Theatre management say it is 'clearly unacceptable' that people felt they could not raise their complaints, and suggests that Mr Spacey operated 'without sufficient accountability'.
The statement adds: "The Old Vic truly apologises for not creating an environment or culture where people felt able to speak freely."
Matthew Warchus, the current artistic director of the theatre, said: "I have genuine and deep sympathy for all those who have come forward and said they were hurt in some way by my predecessor’s actions. Everyone is entitled to work in an environment free from harassment and intimidation.
"The Old Vic is now actively engaged in the process of healing and the process of prevention."
He added: "These allegations have been a shock and a disturbing surprise to many of us. It is incorrect, unfair and irresponsible to say that everybody knew. But as a result of the investigation, what we have learnt is how better to call out this behaviour in future."
Spacey has faced a series of allegations of inappropriate behaviour since actor Anthony Rapp claimed Spacey had made a sexual advance toward him in 1985 - when Rapp was just 14 and Spacey was 26.
Spacey has apologised to Rapp following the allegation, although faced criticism for coming out as gay in the same statement as his apology.
A number of other allegations have subsequently emerged.
The fallout has seen Spacey fired from House of Cards, as well as replaced in an upcoming film only weeks before release.