Only one quarter of sex attack victims reported their ordeal to the Garda, a report has revealed.
The Rape Crisis Network Ireland (RCNI) report for last year showed that just 26% of survivors went to the authorities.
The agency's annual statistics also revealed that more than two-thirds of child sex abuse victims seeking help at its centres had been assaulted by more than one attacker.
Fiona Neary, RCNI director, claimed rape and child sexual abuse remained common and endemic in Ireland.
"Hundreds and hundreds of women, men and teenagers continue to contact Rape Crisis Centres every year in Ireland," she said.
"Most are seeking help for abuse that happened in their childhood, by someone in their family, and that abuse is still affecting their daily lives. For another one-third of survivors they have been raped as an adult."
The RCNI national rape crisis statistics for 2009 also found 89% of perpetrators were known to survivors, while 17% of victims the RCNI dealt with had told no one else about their experience of sexual violence.
13 RCNI member Rape Crisis Centres provided counselling and support to 1,588 people.