Just eight sex offenders in prison completed a programme last year aimed at reducing the risk of reoffending.
Officials in the Irish Prison Service have expressed concern at the low take-up for such programmes.
There are about 280 prisoners serving sentences for sexual offences.
The sex offender programmes are offered in Arbour Hill and the Curragh prisons.
International research shows that those who complete the programmes are almost twice as likely not to reoffend.
Authorities say just a small number are suitably motivated to take part in the programme, although it acknowledges this may also be due to limited one-to-one therapy and the absence of an incentive to participate.
An independent evaluation of the sex offender programme, completed by UCD's psychology department this year, found that it complied with the highest international standards and achieved significant positive changes among men who have successfully completed it.
The Department of Justice says there is no waiting list. All sex offenders are invited to apply for a place on the programme when a new group is being set up.
In a statement, it said every effort was made to assist sex offenders in custody who are willing to participate in personal rehabilitation. More than 100 sex offenders have completed the programme since it was established a decade ago.
The probation and welfare service also organises a Dublin-based programme, in partnership with the Granada Institute, for offenders leaving prison.
The programme is offered to offenders regardless of whether they completed a programme while serving their sentence.
It involves community sex-offender group treatment for men who have offended against children. There are eight places in each programme, and two programmes are run each year.
Meanwhile, plans are under way to implement the Government's policy of creating a drug-free prison service in the new year.
The Irish Prison Service says it will implement a new strategy of mandatory drug testing, addiction counselling and treatment, along with increased measures to prevent drug use.
A drug policy group, including representatives from the prison governors, health boards and medical profession, has drafted proposals for common drugs policies across the prison service.
There are also plans to develop and expand drug treatment programmes, in conjunction with community and health agencies, according to the Irish Prison Service.