People who are sexually assaulted by a family member as a child are more vulnerable to such attacks in adulthood, according to the Rape Crisis Centre (RCC).
A tenth of all survivors of child sexual abuse using RCC services nationwide reported being assaulted in their adult years.
Of those who were victims as children and adults, more than half of the child abuse cases involved family members, according to a report from Rape Crisis Network Ireland (RCNI).
RCNI executive director Fiona Neary said: "For those subjected to sexual violence both as children and as adults, 56 per cent of perpetrators of the child sexual abuse were family members."
The report revealed that 1,626 people sought counselling in 14 RCC services in 2006, 87 per cent of whom were women. Most were aged between 30 and 39, at 29 per cent, while 26 per cent were between the 24 and 29.
It also revealed 67 per cent of adults who were sexually abused knew their attacker. In addition, the report found that 47 pregnancies after rape were recorded. Two-thirds of those opted to keep their babies.
Just over 14 per cent of people reported their abuse to gardaí. RCNI said 52 per cent of sexual abuse victims had revealed details of their experiences to someone else.
The RCNI said the isolation and vulnerability felt by those who were abused by family members leads them to be susceptible to sexual predators later in their lives.
"These findings challenge Irish society to examine how our attitudes to the family may add to the burden of silence a victim of sexual violence carries in Irish society," Ms Neary said.