Wexford, England - The Catholic Church must put in place measures to ensure the safety and welfare of children and young people, the Bishop of Down and Connor has said.
Bishop Patrick Walsh said a report on abuse by 21 priests over 40 years in Wexford made for "shameful reading".
He said it was time "not only to apologise" but to implement "clear policies and strict procedures approved and monitored by outside agencies".
Bishop Walsh said its paramount concern was the safety and welfare of children.
"Child protection must be at the heart and core of all our contact with young people," he added.
On Friday, the diocese released statistics showing that 15 priests have been accused of sex abuse there over the past 50 years.
Northern Ireland's largest Catholic diocese said five priests were dead at the time of the allegations.
Three priests have been convicted and payments totalling £102,000 were made to 10 people because of two priests.
In Sunday's letter, Bishop Walsh said it was "a time for repentance and sadness, but also for resolute action".
"For those who have suffered in this way in our own diocese and throughout the Church, words of apology appear very weak and inadequate and yet must not be left unspoken," he said.
"Our first concern must be to reach out to victims and to ensure that what has happened will never happen again.
"We fully acknowledge the hurt that remains with those who have suffered, not only with the victims themselves but with their families and friends."
Meanwhile, a priest who worked in parishes in Belfast and Lisburn has been speaking of the abuse he suffered at the hands of another clergyman.
Fr Paddy McCafferty, who is a priest of the Diocese of Down and Connor, said he was abused by the priest when he returned to Belfast for his holidays.
"In the system, you really had no rights. There was no-one to turn to for help," he said.
"I felt that I would have been the one who was in trouble and be blamed."
Fr McCafferty, who is now studying for a theology degree in Dublin where he is a parish chaplain, said he felt he could do nothing to stop the abuse.
"People would say 'you were no longer technically a child, why did you not say no'.
"I felt that I couldn't, I felt I had no say - this person was very domineering with a strong personality. He was already a priest, while I was only a student."
The issue of clerical sexual abuse has come to the fore again in recent days following the Ferns inquiry which found that 21 priests had abused children in County Wexford over the past 40 years.
Dioceses on both sides of the border have been releasing figures outlining allegations of child sex abuse throughout the years.