Glen Malcolm Porritt, 24, was found guilty in April of the manslaughter of his mother, Nanette Porritt, at the family's Canberra home in December 2005.

He stabbed her 57 times after the pair got into a heated argument over his request for compensation for perceived suffering during his youth, including the withholding of acne medication.

ACT Supreme Court Chief Justice Terrence Higgins today sentenced Porritt to five years jail with a 22-month minimum term.

Justice Higgins said the sentence was "more severe than any other ... for unlawful homicide" in the cases he had cited.

Taking into account time already served Porritt was released immediately.

Leaving court with his father, Keith, and his sister Jenna, the 24-year-old declined to comment to waiting media.

In a victim impact statement presented to the court earlier this year, Porritt's father said he would welcome his son back to the family home "despite all the grief and suffering".

He acknowledged his wife was short-tempered and a harsh disciplinarian.

Justice Higgins said Porritt "tragically misread the cues his mother gave him on December 21, 2005" because he was battling undiagnosed Aspergers disorder.

On that day Porritt, who was estranged from his parents and did not live with them, told his mother he planned to sue for injustices he experienced as a child.

She demanded he leave the house.

Mrs Porritt then "tragically reinforced her demand by picking up and brandishing a sharp knife", Justice Higgins said today.

Porritt was criminally negligent because he followed her upstairs when she went to call the police and "became trapped in the bedroom".

"His mother, not unnaturally, was seriously alarmed ... and flashed at him with the knife."

In a panicked attempt to leave the room, Porritt then fatally stabbed his mother "negligently unmindful of his then possession of the knife".

The stress of being charged with his mother's murder and being remanded in custody had led to Porritt developing a schizophrenia-type disorder, Justice Higgins said.

The 24-year-old has expressed genuine remorse for his actions, the court heard earlier this year. Porritt told his probation and parole officer: "I should have left the house when she (his mother) asked me to. I didn't. I'm responsible."

His mother's death was a tragedy because she had been trying to make amends and they "could have made peace".

Porritt has been placed under an involuntary mental health treatment order and prescribed anti-psychotic medication.

He has also been placed on a good behaviour order for four years.