A Ballarat bishop buried his head in the sand and didn't think he had to tell police about clergy who sexually abused children, the royal commission has heard.

Convicted Ballarat priest Paul David Ryan says Bishop Ronald Mulkearns knew about him in 1977 but did not revoke his faculties until 1993.

"Ryan thought Bishop Mulkearns buried his head in the sand about the sexual abuse issues in the diocese," senior counsel assisting the commission Gail Furness SC said in her opening address.

She said Bishop Mulkearns also did not think it was his job to tell police about Father Gerald Francis Ridsdale, who abused more than 50 children as he was moved between nine Victorian parishes and church locations.

Ms Furness said it was not until June 1988 that Ridsdale was suspended for 12 months, 13 years after Bishop Mulkearns first knew he was sexually abusing boys he met during his work as a priest.

Ridsdale is believed to have abused every boy aged between 10 and 16 at the school in the town of Mortlake, a royal commission hearing into abuse by Catholic clergy and other church personnel in the Ballarat diocese has heard.

The inquiry heard Bishop Mulkearns told a Catholic Church Insurances investigator in 1993 there were complaints of inappropriate behaviour with young Mortlake boys "so he was taken out of there".

"Bishop Mulkearns told the Catholic Church Insurances investigator that he did not take it as his position to report Ridsdale to police," Ms Furness said.

Ms Furness said there is evidence that Bishop Mulkearns removed a psychiatrist's letter from Ridsdale's file and destroyed it.

Bishop Mulkearns signed a memorandum saying he destroyed the letter from Dr R.E. Seal - dated in the early to mid 1960s - because he thought it was privileged, Ms Furness said.

"He recalled that the letter said that Dr Seal had seen Ridsdale and was confident that, with appropriate care, he could function as a priest in the future," Ms Furness said.

Ms Furness said despite the fact that Ridsdale continued to offend while receiving counselling, no alternative treatment was sought outside the confines of the Catholic Church.

Ms Furness SC said Ridsdale was a prolific offender while parish priest in Mortlake from January 1981.

"There will be evidence that his behaviour around boys was no secret in Mortlake," Ms Furness said on Tuesday.

The commission heard there has been a large number of reported suicides and premature deaths, and significant social, health and mental health issues for survivors in Ballarat.

Abuse survivor Philip Nagle said of the 33 boys pictured in his 1974 grade four class photograph at St Alipius Primary School, 12 have died. He believed they committed suicide.

Ridsdale will give evidence during the three-week Ballarat hearing while Ryan has given evidence in a private hearing.