Ten registered sex offenders, including nine paedophiles, have gone missing from Sussex, police figures have revealed.
Seven of those are thought to be have gone abroad, including one deemed to be a high risk of reoffending.
A Freedom of Information Act request by BBC South also showed that three offenders were missing in the UK.
Sussex Police said they made every effort to track down sex offenders who disappeared.
BBC South used the Freedom of Information Act to obtain figures from the Dorset, Hampshire, Sussex, Surrey, Thames Valley and Wiltshire police forces.
Campaigner Christine Beddoe, director of child protection charity Ecpat UK, said: "It's absolutely shocking that dozens of sex offenders have gone missing in the South, many of them paedophile sex offenders.
"And we know that if they've abused children here and they've gone missing, gone abroad, they'll definitely be abusing children abroad.
Those that tend to go missing... tend to go abroad because it's more difficult for us to track them down and bring them back
Det Ch Insp Neville Kemp
"We want the police to do much more. We think that by working with policing contacts abroad, by working in joint investigation teams and by working with organisations like ours and similar organisations abroad, we can do much more."
Sussex Police Det Ch Insp Neville Kemp said although the figure might seem high it represented about 1% of the total number of people on the register in Sussex.
He added: "[The figure] actually says that 99% we know where they are, we have some sort control over them, they're being properly monitored. It's actually a testament to the robustness of the process.
"Those that tend to go missing, and make a determined effort to do so, do tend to go abroad because it's more difficult for us to track them down and bring them back.
"We do make every effort to locate them and we work closely with CEOP (Child Exploitation Online Protection Agency), Interpol and then various agencies within the host country to bring them back.
"Quite often we don't have to use the extradition route because it will be the case that they've entered the country and not declared their criminal convictions and actually committed immigration offences in that country."
Mr Kemp said that the cases of those that do go missing were reviewed at least every 16 weeks and specialist officers dealt with bodies such as public utilities and international agencies to try to trace the offenders.
There were 941 people on the sex offenders register living in Sussex, according to Ministry of Justice figures for 2008/2009.
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