The bishop of the Belgian city of Bruges, Roger Vangheluwe, has resigned after admitting sexual abuse of a boy earlier in his career.
Bishop Vangheluwe, 73, said the abuse had happened when he was a simple priest and continued when he started as a bishop, a Vatican statement said.
The Vatican said Pope Benedict XVI had accepted the resignation.
The Catholic Church has come under severe pressure over child sexual abuse allegations emerging across the world.
The BBC's David Willey, in Rome, says the Pope's acceptance of the bishop's resignation marks a new escalation in the scandal buffeting the Church.
It is the first time that a senior churchman has admitted in person abusing a child, he says.
"When I was not yet a bishop, and some time later, I abused a boy," Bishop Vangheluwe said in a letter that was read out at a press conference in Brussels.
"This has marked the victim forever. The wound does not heal. Neither in me nor the victim."
Bishop Vangheluwe added that he was "enormously sorry" and that he had repeatedly asked for forgiveness. He had been bishop of Bruges since 1984.
'Turning a page'
Belgium's Archbishop Andre-Joseph Leonard told the press conference in Brussels that the case would be "very saddening to the Belgian Catholic community".
"We are aware of the crisis of confidence that this will engender for a number of people," he said.
But he said the resignation showed that the Belgian Catholic Church wanted to "resolutely turn a page on a very painful" topic.
Bishop Vangheluwe's decision to quit comes after the announcement earlier this month that a German-born former Roman Catholic bishop in Norway, Georg Mueller, had resigned last year after admitting to committing sex abuse.
This week there have been a series of resignations offered or accepted by bishops who were not accused of committing sex abuse.
It was announced on Thursday that the German Bishop of Augsburg, who had been accused of beating children at a Catholic children's home in the 1970s and 1980s, had tendered his resignation.
Bishop Walter Mixa had also been under pressure over allegations of financial irregularities at a children's school under his responsibility.
This week the Pope also accepted the resignation of Bishop James Moriarty of Kildare in Ireland, who said he wanted to play a part in creating a "new beginning" following scandals there.
Bishop Moriarty was one of several Irish bishops to resign after the Church was criticised over its handling of abuse cases.
The Pope promised "action" over abuse against children by priests when he met victims during a visit to Malta last week.
In Germany, where recent allegations have caused widespread anger, Church representatives were among those participating in a round-table discussion on Friday about widespread abuse in schools and other institutions.
The event, which aims to encourage justice for victims and prevention of future abuse, brought together about 60 people including politicians, lawyers, psychologists and representatives of teachers' organisations.
"Whether it occurs in Church institutions, schools, or in familiar circles, there are conspiracies of silence everywhere," Christine Bergmann, the government commissioner who was chairing the session, was quoted as saying by German broadcaster Deutsche Welle.
Meanwhile, the Vatican on Friday rejected a US lawsuit brought by a man who says he was the victim of the late Father Lawrence Murphy, accused of abuse at a school for deaf children in Milwaukee.
Vatican lawyer Jeffrey Lena said the suit was "completely without merit" and rehashed "old theories already rejected by US courts".