Terry Williamson leaves Silverwater jail in 2012.

Terry Williamson leaves Silverwater jail in 2012. Photo: Dave Tease

Convicted rapist Terry John Williamson will spend another five years under the supervision of parole authorities after the NSW Supreme Court accepted he was a high-risk sex offender whose release from prison warranted prolonged precautions.

The extended supervision order took effect from 10pm on Thursday, replacing an interim order that was to expire on July 9.

In extending the order for the maximum possible term, Justice Peter Johnson considered Williamson's relative youth (he will turn 45 next week) and that, having spent more than half his life behind bars, he had been given limited opportunity to show he could live in the community without reoffending.

Justice Johnson also considered reports by court-appointed psychologists which indicated that Williamson's behaviour since his release on parole back in February 2012 had been controlled by anti-libidinal medication.

"The evidence reveals that there's a significant increased risk of the defendant reoffending if anti-libidinal medication is ceased. [The medication] is an important part of the management of the risk he poses to the community," he said.

The extended order requires Williamson to continue taking the drugs, and any others prescribed by a medical practitioner.

He will also be required to wear electronic monitoring equipment for the duration of the order.

"A guarded, long-term approach is required with respect of this defendant, having regard to the gravity of the crimes committed," Justice Johnson said.

"I accept that if the defendant did reoffend there is a prospect of very serious offences being committed.

"There is no sign of that at present, nor has there been for two years, but that, in my view, is [due to] the intensive treatment and supervision regime which is applied to him, and which should continue to apply."

The order does not prohibit Williamson from entering the Illawarra, but states he "must not frequent or visit any place or areas specified by the departmental supervising officer".

He must notify authorities if he wants to start a new job or if he forms a sexual relationship.

Restrictions also apply to his use of the internet, and he is not allowed to join any social networking communities.

Williamson spent 22 years in prison for a string of brutal rapes and sexual assaults, beginning with the rape of a 13-year-old girl on the grounds of Bulli High School on August 5, 1989.

In the 10 months that followed, Williamson assaulted another nine females aged between five and 44, and an 11-year-old boy.

Justice Johnson considered statements from five of Williamson's victims before determining a prolonged supervision order was warranted.