A serial rapist who terrorised women in Perth's western suburbs in the 1980s has been kept in jail indefinitely after a judge found there was an unacceptable risk he would commit more sex crimes if released.

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No parole for serial rapist
Dennis Lyddieth leaving court in 1992. Picture: Mal Fairlclough/The West Australian

A serial rapist who terrorised women in Perth's western suburbs in the 1980s has been kept in jail indefinitely after a judge found there was an unacceptable risk he would commit more sex crimes if released.

Dennis John Lyddieth was this morning declared a dangerous sex offender and deemed unsuitable for release into the community even under special conditions.

The move means the 61-year-old, who has spent almost 20 years behind bars and was due for release last month, will stay in jail with an annual review of his situation conducted each year.

Lyddieth raped nine women and tied up and threatened some of his victims with knives between 1987 and 1991.

He had fought the State's move to declare him a dangerous sex offender.

Today, Justice Stephen Hall ruled that Lyddieth was at a moderate to high risk of committing further sex offences if he was not subjected to a detention order or supervision order.

This was because of a lack of an appropriate release plan, Lyddieth's failure to significantly change his behaviour, and a proven failure to use support services.

Lyddieth had been released on parole in 2002 but committed further crimes that saw him returned to jail.

Justice Hall accepted that research indicated Lyddieth's age may have lessened his risk to the community. But he found the risk he posed to the community was still significant especially as it related to "all women, particularly younger women" and was not restricted to a small class of potential victims.

"In my view, there are no conditions that would either be effective or adequate to manage the risk that Mr Lyddieth presents, or reduce it to an acceptable level," Justice Hall said in his judgment.

The judge noted there were treatments behind bars that could be used by Lyddieth to reduce the risk.

Lyddieth is in Casuarina Prison.