A teenager from NI who abused other children has been treated at a specialist treatment centre in the UK at a cost of £1.5m.
He was treated there because the help needed to treat his sexually abusive behaviour is not available in NI.
The teenager spent over three years receiving help before returning to NI.
The case was highlighted by the the investigative news organisation, The Detail.
The boy's local health trust paid the bill. His mother and a social worker were flown over to visit him once a month during his stay at the residential centre.
It is understand that millions of pounds is spent every year on similar treatment programmes for young people from NI who are displaying harmful sexual behaviour.
Consultant forensic psychiatrist, Dr Ian Bownes, works with teenagers and children who are displaying inappropriate sexual behaviour.
He said the results from the treatment outweighed the cost.
"The cost of the private treatment centres is usually money well spent, although they will also require an extensive follow-up programme when they come back," he said.
"Chaotic home lives"
"We have no choice but to send these young people to a specialist unit. It is very rare that someone starts this kind of behaviour at age 12 and that it keeps building up until they become a predatory rapist or paedophile but we cannot take the risk of leaving their behaviour untreated.
"These children are taken away from their often chaotic home lives for two or three years and this gets them through their adolescent period. It is really only after this that we will know what we are dealing with.
"Running parallel to their sexualised behaviour are often other issues like stealing cars, using drugs and getting into fights. There are often many variables and sexually inappropriate behaviour is just one of many factors."
Dr John Devaney from the School of Sociology, Social Policy and Social Work at Queen's University in Belfast said there is a small number of services in NI able to provide help to young people displaying sexual behaviour.
"Research tells us that the earlier we recognise the risk that these young people present, and provide them with intensive and very structured therapeutic interventions, the greater the likelihood that they can be supported to desist from this behaviour," he said.
"There is evidence that they are making an important difference.
"However the funding for these services is limited but we know that if young people who display sexually inappropriate behaviour are not worked with then their behaviour becomes more entrenched and much more difficult to deal with later."
Around half of all adult sex offenders commit their first offence as a juvenile.