Cardinal George Pell has admitted he did nothing after a boy complained to him about a pedophile Christian Brother abusing children at a Victorian school but denied he could have stopped more abuse occurring.

The child abuse royal commission has heard a student at St Patricks College in Ballarat told Cardinal Pell that Brother Edward Dowlan was "misbehaving" with boys in 1974.

Cardinal Pell said the boy "mentioned it casually in conversation" and did not ask him to do anything.

Asked by Commissioner Peter McClellan what he did with the information, Cardinal Pell replied: "I didn't do anything about it".

Eventually, he said, he inquired about the matter with the school chaplain but did not go immediately to the school to find out what was going on.

"With the experience of 40 years later, certainly I would agree that I should have done more," Cardinal Pell said.

Lawyer Peter O'Brien, representing a former student of the Christian Brothers from Ballarat, asked Cardinal Pell "why on earth" he did not mention the complaint to police or insurance companies involved in cases brought against the Christian Brothers about Dowlan since the 1990s.

"Why do we hear about it this week for the first time?" Mr O'Brien asked.

Cardinal Pell said it was because he had "no idea that the Christian Brothers were covering up in the way in which it's now apparent".

Dowlan continued to abuse dozens of children until 1985 But Cardinal Pell said he could not have done something to stop the crimes.

He said he did not withhold information and rejected the suggestion he was "in the business ... of trying to minimise your own involvement".

Mr O'Brien said Cardinal Pell had "pointed the finger at other people" and was prepared to deny the truthful accusation his client had made against him.

Cardinal Pell rejected the claim and said the accusation - that he had ignored another complaint about Dowlan beating a boy - was "demonstrably false".