Catholic leaders from around the world gathered on Monday for an unprecedented Vatican summit to find ways to root out paedophilia in the clergy that came under heavy criticism from victims.
Bishops from 100 countries and the leaders of 33 religious orders will take part in the four-day meeting, as well as the Vatican's anti-abuse prosecutor Charles Scicluna and just one abuse victim, Ireland's Marie Collins.
Pope Benedict XVI is expected to issue a special blessing for the closed-door conference, which will also launch a child protection centre in Germany to fight sex abuse by the clergy in the Church worldwide.
The symposium, entitled "Towards Healing and Renewal", will also include a church service on Tuesday in which representatives of seven religious orders which had paedophile clergy in their midst will plead for forgiveness.
Victims' groups said they were not invited and slammed it as a PR stunt.
"You don't need a jolly in Rome to learn what the right thing to do is," said Sue Cox from Survivors Voice, a coalition of victim support groups covering Britain, Germany, Ireland, the Netherlands and the United States.
"This is just a PR stunt. It's just theatre really. It's no use whatsoever," Cox, herself a victim of abuse by a priest who says she still gets panic attacks from the smell of "whisky, incense and stale sweat", told AFP.
Roberto Mirabile, head of the Italian victims support group La Caramella Buona, said: "You can have all the symposiums you want but why don't you open a constructive debate. The Church is too closed in on itself."
The meeting starts at 1730 GMT with a keynote speech by Cardinal William Levada, the head of the Congregation for the Doctrine of the Faith, the top enforcement body of the Catholic Church which has led efforts against abuse.
The Vatican has requested that all the national bishops' conferences of the world must submit by May a set of comprehensive guidelines on how to combat paedophilia, stressing that abuse is not only a problem for Western churches.
But officials say some countries are having trouble formulating these rules because of "cultural differences" over what exactly constitutes child abuse and victim support groups say the measures lack any real enforcement powers.
Father Hans Zollner, a Jesuit priest and psychotherapist who heads up the new Centre for Child Protection, said on Vatican Radio on Monday ahead of the start of the conference: "The best measure is to listen to the suffering."
Bishops attending the meeting have been asked to hold "listening sessions" with abuse victims before travelling to Rome to help them understand and psychologists and child health experts will address the conference.
Francois-Xavier Dumortier, rector of the Gregorian University, said: "This is a crucial problem for the Church.
"The pope has taken a very clear and I think very courageous position not to skate over the surface of the problem but to go deeper."
"We want to provide all the means to prevent the problem," he said.
Dumortier stressed the importance of training for men and women of the clergy, including the 2,000 students at his university.
"We have a major responsibility to look at this open wound in the Church with open eyes and try to do everything so it does not happen again," he said.
Collins, who was raped by a priest in a hospital in Dublin when she was a little girl and has become a leading voice in pushing for justice for victims in Ireland, said her decision to attend was not an easy one.
"Despite apologies for the actions of the abusers, there have been few apologies for protection given to them by their superiors," she said earlier.
"There seems to be a lack of penalty for any of these men in leadership who deliberately or negligently covered up for abusers," she added.
The Roman Catholic Church has been rocked in recent years by thousands of paedophilia scandals, some of them dating back decades.
Cases of abusive priests and cover-ups began to go public in Ireland and the United States but have since been reported across much of Europe.
Officials say there is also a hidden abuse crisis in parts of Africa, Asia and Latin America.