The government has admitted in the House of Lords that it cannot say how many registered sex offenders may be working with children in the NHS.
Lord Warner was quizzed in the House of Lords
The admission comes after last week's row over revelations some registered child sex offenders had been allowed to work in schools.
Peers had pressed the government to ask if there could be similar problems hidden in the health service.
Health Minister Lord Warner said NHS trusts decided who was checked.
He told peers checks on all new NHS staff with access to patients were compulsory against the criminal record bureau, and there were extra checks for those working closely with children.
These checks would include all child specialist and paediatric services, but the exact posts covered by the extra checks would be decided by the local employers.
Tory Lady Seccombe, who had raised the issue, said this all still sounded very "confusing and concerning".
She pressed the minister to say how many people cautioned for, or convicted of, a serious sexual offence were working in the NHS and what was he doing about it?
Lord Warner said he didn't have the exact figures.
This was "a complex area" and the government "knew there were problems".
He said the government had "done its utmost to ensure that all these people do not have access to children".
And he insisted that the new law promised by Education Secretary Ruth Kelly last week would "close a number loopholes".
Pressed again by the Tories to say how many registered sex offenders were working with children in the NHS, Lord Warner said there were some 600 different employers in the NHS and he had "given the answer which he thought was appropriate".
Shadow Health Secretary Andrew Lansley said there were serious questions the government had to answer.
"It is clear that it does not know how many individuals employed in the NHS and social care sectors have committed a sexual offence against children.
"This makes it imperative that the list which individual NHS and social care organisations make checks against is as comprehensive as possible.
"The current health and social care equivalent to education's List 99, the Protection of Children Act list, is not comprehensive."