Priest John Denham abused more than 50 children in parishes across NSW, a court has heard.
For years a Catholic priest viewed a NSW school where he taught as a "pedophilic smorgasbord" catering to his depraved desires.
Unfettered by the church, John Sidney Denham abused dozens of boys whenever and wherever he chose.
He found new victims during his frequent transfers to parishes across the state.
Denham, at 73, is already in the middle of a jail term, handed to him in 2010 for his sexual assault of boys as young as five.
But on Friday, Judge Helen Syme sentenced the priest to another 13 years jail for charges stemming from his abuse of 18 boys at St Pius X in the Hunter in the 1970s.
"Some of the offences represent the most abhorrent and sadistic combination of circumstances that courts are likely to see," she said.
Adding the new charges, Judge Syme calculated Denham had abused 57 children, some repeatedly.
"At St Pius X, the offender operated as if he was at some pedophilic smorgasbord, entitled to abuse boys at any time or place of his choosing," she told the Downing Centre District Court in Sydney.
"It defies belief that his abuse of children was not only widely known but ignored or condoned by those in authority."
Denham's victims intermittently left in tears as the court heard how he preyed on the most vulnerable boys.
He would befriend the child, give them treats, abuse them and then threaten them.
The priest seemed to relish how their vulnerability increased by his abuse, by smirking and making flippant comments, she said.
The boys were attacked in public and private - in the playground, in the principal's office and even outside the confessional.
If the boys complained to the now-dead principal, Father Tom Brennan, further physical abuse ensued.
Denham has told a psychologist he had received "oblique warnings" while at St Pius X, and was told "the fathers don't like that kind of thing".
But nothing was done.
Instead, frequent transfers between parishes including Mayfield, Singleton and Taree, allowed him to gain access to new victims.
In 1994, the Newcastle Maitland Diocese directed that he should not work with children, but he continued to operate within the church, without investigation.
The protection offered by his co-workers meant Denham had "a remarkable 18 years of uninterrupted offending in several parishes", Judge Syme said.
The effect on the victims has been catastrophic, with many suffering from relationship breakdowns, substance abuse and mental illness.
The school was described as a place where punishment was meted out mercilessly and Denham's sadistic behaviour contributed to its climate of fear.
For the abuse of 18 boys at the school, Denham was sentenced to at least 13 years and a maximum of 18 years.
This will be served at the same time as his 2010 sentence, so he will be eligible for parole in 2028.
Speaking outside court, one of Denham's victims, who did not want to be identified, said the Catholic Church should be accountable.
"My life starts today and it starts for a brighter future," he said.