The vast majority of sex abuse survivors who sought help in Rape Crisis Centres last year were attacked as children.
Of the 2,308 people who went for counselling, 53% of the women and 84% of the men reported the violence occurred when they were children only.
Some 65% of survivors said they were abused aged younger than 12.
The Rape Crisis Network of Ireland (RCNI) revealed that those who came forward last year had waited on average 25 years to access its services.
Fiona Neary, RCNI director, said the figures showed the need for strong legal and social supports to protect vulnerable children.
"While the family unit is usually the best place for children, these statistics show that it can also be the most dangerous place," she said. "Legal protections and adequate resources must be put in place to make the family a safer place and to ensure that children can be heard when they are still children."
RCNI has seen a year on year increase in people seeking vital support, but last year funding from the Health Service Executive fell by 4.7%.
Ms Neary said the statistics demonstrated the need to combine data collection with strengthened services for today's sex abuse survivors and survivors of the past who remain silent. On average adult abuse survivors can take up to five years to report sexual violence to the RCNI.
The 2011 statistics, to be released in full in Galway on Friday at the third International Conference on Survivors of Rape, reveal that the home was the most dangerous place for sex attacks.
The RCNI said that in total 2,541 people came forward to take up counselling and support in 2011 - an 11% increase on the previous year. The RCNI is supporting a Yes vote in the weekend referendum on children's rights. The agency also warned that RCNI members worked more than 1,900 hours a week to meet the increasing demand for services last year. More than 17% of the work was done by volunteers, which the RCNI said is unsustainable.