John Clayton Sims, 44, was arrested in South Australia on Monday and extradited to Sydney on Wednesday night where he was charged over the 1996 attack which left the then 19-year-old woman in hospital with a facial fractures and a brain injury.

The young woman had been partying with friends at the now-closed Kicks nightclub in Parramatta on March 8 1996, when Mr Sims allegedly approached her and struck up a conversation.

Believing Mr Sims knew her boyfriend, the teenager left the club with him and continued chatting with him in the car park. But once outside, the conversation quickly disintegrated as Mr Sims became violent, police will allege.

He then allegedly "viciously and horrifically" assaulted her, fracturing her face and leaving her with a brain injury, Detective Inspector Michael Haddow from the NSW Police Sex Crimes Squad said on Thursday.

She lay bleeding and unconscious in the car park for several hours until she was found about 3am by police patrolling the area.

"These injuries were very, very significant and, like any injury, it takes a long time to heal the physical scars but the mental scars continue."

For two decades, NSW Police were unable to identify a single suspect in connection with the attack.

Then, in November last year - after the investigation was handed to the Sex Crimes Squad - further forensic analysis of crime scene samples from 1996 gave police the break they were looking for.

Detective Inspector Haddow said considerable advancements in forensic technology over the past two decades, in combination with traditional detective work led police to arrest Mr Sims, who was not considered a suspect in 1996.

He said cases like this sent a clear message to offenders: "These matters don't go away.

"It's absolutely important to be able to give the victim answers. Matters like this stay with victims forever."

The woman, who is now 38, was "very pleased with the result" and wanted to continue "to get on with her life", he said.

Mr Sims, who now lives in Adelaide, was flown to Sydney under police guard on Wednesday night, where he was charged with aggravated sexual assault, maliciously inflicting grievous bodily harm, and inflicting actual bodily harm with intent to have sexual intercourse.

He did not apply for bail and it was formally refused in Central Local Court on Thursday.