More than 100 woman were raped, sexually assaulted or sexually harassed in NHS mental units over two years, a study is believed to have found.
The results are described as "extremely disturbing"
The report was passed to the Department of Health eight months ago, and has yet to be published.
However, the Times newspaper says it includes details of more than 10 rapes - at least three leading to pregnancy.
Officials said the report was still being finalised, and it would be published as soon as it was complete.
But Paul Farmer, chief executive of mental health charity Mind, demanded the report be published immediately - and a review set up to establish the full extent of the problem.
The information is believed to have been compiled by the National Learning and Reporting System - a monitoring programme set up by the National Patient Safety Agency in 2003.
Most of the reported incidents were said to have occurred in the 12 months up to October 2005.
The country's 84 mental health trusts were among the last bodies to sign up to the system that is supposed to cover all healthcare organisations.
The report is said to include both patient-on-patient and staff-on-patient incidents.
They ranged from men exposing themselves to women through to physical assaults and rape.
Mr Farmer described the findings as "extremely disturbing".
He said that with many safety incidents in the NHS going unreported, the actual picture could be much worse.
Mind has put in a Freedom of Information request calling on the government to issue the report immediately.
Mr Farmer said: "People who work inside the mental health sector, and outside the mental health sector, will be extremely shocked that this seems to be taking place.
"We are talking about very vulnerable people, who are in in-patient units to receive care and treatment for their mental health problems, being exposed to sexual assaults and rapes.
"We need a systematic review to find out what the true scale of this is.
"Is this the tip of the iceberg or is this the whole iceberg?"
Mr Farmer said his charity had heard that the rules stipulating that men and women were kept on separate wards in mental health units were "being bent".
This, he warned, could compromise patient safety.
Sandra Gidley, Liberal Democrat health spokesperson, has tabled a parliamentary question calling for the report to be published immediately.
She said: "Urgent steps must be taken to stop sexual abuse of any kind in mental health settings and ensure that nobody is being treated on mixed sex wards.
"This is essential as they are amongst the most vulnerable in our society."
Lynne Jones, co-chair of the All Party Parliamentary Group on Mental
Health, said the research backed up what was already known.
"In wards that should be the safest of all, the problems are worst.
"We put trust in the NHS to look after vulnerable people, sometimes against their own will, yet many of them are being put into a dangerous situation when they go into hospital. Our trust and theirs is too often betrayed."
The Department of Health refused to comment on the details of an unpublished report.
However, in a statement it said work was needed to clarify some of the points in the report, and to ensure it accurately reflected the complete picture.
It also said it would expect all trusts to thoroughly investigate any allegations of sexual assault, and to involve the police where necessary.