In a case described to be a first in Ontario, a repeat rapist has been spared an indefinite prison sentence because he suffers from fetal alcohol syndrome.

Superior Court Justice Fran Kiteley ruled against labelling Wayne Mumford a dangerous offender, and instead told him to "work hard" on bettering himself while incarcerated.

Mumford, 31, has spent nearly all of his adult life in jail for violent sexual assaults against strangers and family members. Some of his victims were female prison guards, court heard.

Mumford's lawyer, Paula Rochman, said her client suffered a brain injury because his mother drank while she was pregnant. The result has left him with the IQ of an eight-year-old, court heard.

"This is a person who does not want to reoffend, he does not like it," Rochman said. "When he speaks about it, he's quite upset by his own behaviour. He wants to change his behaviour."

Court heard Mumford was also sexually abused by his father, HIV-infected pedophile Donald Mumford, who sparked a community backlash in Toronto's Parkdale community in 2002 when he attempted to relocate there after being released from jail.

Wayne Mumford wept in the prisoner's dock on Tuesday when the judge spared him dangerous offender status, which would have kept him behind bars indefinitely.

"Thank-you for giving me another chance," he said. "I promise to work very hard."

Crown attorney Cara Sweeny had argued for the dangerous offender designation because she said Mumford is a violent man who can't control his impulses.

"He a very dangerous person and should he reoffend, it's predicted that he'd offend both sexually and violently," Sweeny said.

Mumford was instead sentenced to 10 years in prison. He will be on parole for 10 years following his release.

Mumford will receive treatment in prison, but fetal alcohol syndrome is not curable, only manageable.

The judge urged him to undergo chemical castration, a form of temporary castration caused by hormonal drugs that is believed to lower or eliminate sexual impulses.

With a report from CTV's Chris Eby