Sex offenders' register removal concern for campaigners
North Wales Police removed the highest percentage of convicted sex offenders from the register in the past four years - higher than any other UK force.
Since 2012, 679 criminals in the UK were told they no longer had to register with the police, figures released to the BBC show.
North Wales Police approved 90% of requests, while neighbouring Dyfed-Powys Police did not approve any.
Campaigners said they found the figures "worrying".
Across Wales, 55 requests by criminals to be removed from the sex offenders register were approved, according to figures obtained from 40 out of 44 UK police forces following a Freedom of Information request.
Gwent Police approved 65% of requests and South Wales Police approved 57%.
It comes after the Supreme Court ruled in 2010 that under human rights laws offenders in England and Wales should have the opportunity to prove they had reformed.
At the time of the ruling, Home Secretary Teresa May said: "We will deliberately set the bar for those appeals as high as possible. Public protection must come first."
But, according to BBC Home Affairs Correspondent Danny Shaw, the figures appear to demonstrate that police are interpreting guidance very differently.
"How else can you explain the huge variations between North Wales, where 90% of requests not to register with police succeeded and Dyfed-Powys where none did," he said.
Kevin Hogg, director of Victim Care, a charity set up to support victims of crime, said he was "massively" concerned by the figures.
"The situation as it stands is there to protect the public but they're protecting the offender so much more," he said.
"It really worries me the police are allowing this to happen."
A spokesman for North Wales Police said removals from the register are only authorised after a senior officer has reviewed the case.
A Home Office spokesman said: "Public safety is at the heart of all decisions taken by police.
"Those who continue to pose a risk will remain on the sex offenders register - if necessary, for life."