Mary Louise Wallace, who worked as a nurse at Hunters Hill Private Hospital, disappeared on a night out with friends at a bar in Crows Nest on September 24, 1983.

Police said the popular 33-year-old, from Drummoyne, had been befriended at the Alpine Inn wine bar by Robert Adams, who offered her a lift home.

She was never seen again, and her body has never been found.

Early on Friday, detectives from the Homicide Squad's Unsolved Homicide Team arrested Mr Adams, now aged 61, in Gladesville.

He was taken to Parramatta police station, where detectives charged him with the murder of Ms Wallace.

The arrest is the culmination of 30 years of investigations, including the force's biggest homicide investigation, coronial inquests, re-investigations, excavations and hundreds of interviews.

Detective Superintendent Mick Willing, from the Homicide Squad, said this was the oldest case in which an arrest had been made by the Unsolved Homicide Team.

"This case is an example of exactly why the Unsolved Homicide Team was established with an investigative arm in 2008,'' he said.

"It also illustrates that we will continue working on theses cases for however long it takes to get results, and sometimes even decades later we will come knocking on the door."

Detective Chief Inspector John Lehmann, from the Unsolved Homicide Squad, said DNA evidence would form part of the case.

"There is forensic evidence. We have compiled a number of witness statements that are very important to our brief of evidence. There is physical evidence, scientific evidence that will include DNA," he said.

"It's a credit to the investigators who have put in tireless hours. It's very satisfying for us, but even more so for the family and close friends that were left behind."

Last year, Ms Wallace's sister, Anne Fraser, pleaded for information about her sister's disappearance as police announced a $100,000 reward for information.

At the time, Ms Fraser said the fact that no one had ever been charged over the disappearance of her sister had haunted her.

"I think that's why I'm so emotional," she said. "Because we have never known. If even 20 years ago it had been cleared up, it would be different. I wouldn't be here, a quivering mess, because there is resolution and then you grieve ... and it makes it much easier."

Ms Wallace's parents both died without knowing what happened to their daughter.

In the 1980s, police received an anonymous letter claiming that Ms Wallace's body was buried under a rock in the Lane Cove National Park.

Yet two operations in the national park, including extensive geo-radar testing and excavation in 2010, found nothing. Ms Wallace's body has never been found.

Police said Mr Adams would appear in Parramatta Local Court on Friday.