A former Department of Human Services disability support worker whose lawyer said he was deeply religious and in denial about this sexuality has admitted abusing a series of male patients over 13 years across Melbourne's east.

Craig Handasyde, 47, of Croydon, pleaded guilty in the Victorian County Court to 11 charges of committing an indecent act with a cognitively impaired person by a worker.

Key points: Craig Handasyde pleaded guilty to 11 charges

Craig Handasyde pleaded guilty to 11 charges Victims were blind, deaf and unable to communicate

Victims were blind, deaf and unable to communicate Handasyde wanted to appear to be a happily married heterosexual man, court heard

Handasyde wanted to appear to be a happily married heterosexual man, court heard Victim became "very disturbed" after abuse

The abuse occurred across residential facilities in a number of suburbs, and in some cases involved long-term clients between 1998 and 2011.

Most of his victims, aged in their 20s, 30s, 40s and 50s, were unable to properly communicate and some were deaf, blind and could not talk.

Handasyde also abused his victims at swimming pools, in showers and in one case a motel, during outings or "reward" trips "put in place by the DHS".

In some instances of abuse, Handasyde would walk around the DHS facilities naked and get into bed with his victims as they lay helpless.

On at least one occasion he ignored repeated attempts by one victim to push him away.

The court heard Handasyde was a highly qualified disability development services officer with an advanced diploma in disability work.

He had also undertaken a range of extra courses over the years, including "dual disability" and "communications about behaviour for better outcomes".

Handasyde resigned from the DHS in 2013.

He handed himself in to the sex crimes unit at the Knox police station last year because he "wanted to make admissions about sexually abusing DHS clients over 13 years".

The court heard Handasyde was a religious man who wanted to clear his conscience in the eyes of God.

Two pastors were among 13 people to provide references for him.

'A happily married heterosexual man'

Handasyde's lawyer Paul Higham told the court his client was deeply religious.

He was also homosexual, Mr Higham said, but was intent on presenting himself publicly as "a happily married, heterosexual Christian father," leading to a secret life.

The court heard Handasyde met his wife within the church and wrote her a letter before they got married, telling her he was "same-sex attracted".

"She struggled to accept it, but accept it she did," said Mr Higham.

The couple had eight children who were home-schooled and the court heard Handasyde's wife believed sex was for procreation only.

"What emerges is a picture of a man who is extremely passive and lacks the ability to assert himself," Mr Higham told the court.

Mr Higham said Handasyde "prefers harmony over conflict", and described his client's denial of a large part of his identity as "a tragedy".

Handasyde's wife was in court and wept as their home life was detailed to the families of her husband's victims.

'I trusted you with my son': Mother of victim

The courtroom was packed with the parents and relatives of the men Handasyde's had abused.

The mother of one victim told the court Handasyde's offending had turned her son into a "very disturbed young man".

"Craig Handasyde ruined his happy nature," she said.

"Craig, you were meant to look after him, not cause him distress.

"You were meant to care for him, not abuse him."

The woman told Handasyde she had welcomed him into her family's home on many occasions and felt betrayed.

"You enjoyed our food and hospitality as a thank you for bringing him home," she said.

"I always worried whether I'd done the right thing, sending him to Melbourne.

"You've proved me right. I trusted you with my son who I love so much."

The father of another victim told the court his son "could not even understand simple verbal statements" and would "never be able to care for himself".

The man said he and his wife entrusted their son to a trusted care provider in the DHS and "for many years we thought he was safe".

"We are very disturbed," the victim's father said.

"We can't ask him about how he felt ... the thought of what he [Handasyde] might have been doing ... the real torture is not knowing."

The victim's father told the court, he and his wife had noticed a marked change in their son's mental state 15 years ago, when he became more aggressive.

"At the time, there was no reason for his behaviour change," he said.

"In hindsight, we now wonder if he could have been affected by sexual abuse."

He told the court, his son would not have been able to tell anyone about the abuse or warn others who were vulnerable and exposed.

Handasyde is expected to be sentenced at a later date.