It costs €5,500 to complete a two-and-a-half year rehabilitation course at One in Four, but the HSE is not funding the organisation to provide the treatment.
One in Four says about 60% of people eventually get partial funding from the HSE, paying for the remainder themselves.
However, those who cannot access HSE funding have to find the €5,500 or forget about rehabilitation.
“Research consistently shows that effective treatment programmes reduce the risk of re-offending, yet most sex offenders in Ireland do not have access to treatment,” said Maeve Lewis, the group’s executive director.
“We also know that many sex offenders will continue to abuse throughout their lives until they are caught. While good programmes are available in prison, fewer than 5% of sex offenders will ever be convicted of their crimes.
“There is a huge need for treatment in the community.”
Following the closure of the Granada Institute last year, adult sex offender treatment is limited to the Cosc service in Donegal and the One in Four service in Dublin.
Launching their annual report today, One in Four revealed that it provided treatment to 28 offenders last year. The organisation has a waiting list for its next programme.
Ms Lewis also criticised the criminal justice system, saying many of the one in four who experience sexual abuse find the legal process “humiliating, abusive, and traumatic”.