Petra Pazsitka, now 55, had diapered in 1984 but was found in Düsseldorf, a city in western Germany in early September.
According to reports, Pazsitka was living at a student in the German city of Braunschweig while studying.
In 1984, when she failed to attend her brother's birthday party, police launched a massive search that failed to locate her.
NBC news reports that the police later arrested a man suspected of the rape murder of a 14-year-old girl who later confessed to killing the student.
But her body was never found.
In 1898, the case was closed and Pazsitka was registered dead until she discovered by police who responded to a burglary report at her house.
Police say Pazsitka confessed that her disappearance was deliberate.
She had saved 20,000 euros (N4.5m) to create a new life.
A spokesperson for Braunschweig and Wolfsburg Police quoted by Fox News said she did not explain the reason for her action.
"As to the motive of her disappearance, she gave no explanation and expressly said that she continues to want no contact with the public or her family," the spokesperson said.
Pazsitka has not been accused of any crime, but she will be compelled to register with the authorities as a living person.