Mr Demjanjuk says he was a prisoner of war of the Nazis during World War II
Prosecutors in Germany have formally charged alleged Nazi war criminal John Demjanjuk with 27,900 counts of being an accessory to murder in World War II.
The prosecutors' office in Munich said the charges had been filed on Monday.
There was no immediate word on when the trial of the 89-year-old retired car worker, who was deported from the United States in May, might begin.
Mr Demjanjuk has denied accusations that he was a guard at the Sobibor death camp and helped murder Jews.
He says he was captured by Germans in his native Ukraine while fighting for the Red Army and kept as a prisoner of war.
The formal filing of charges on Monday came 10 days after medical experts at Munich's Stadelheim prison declared that Mr Demjanjuk was fit to stand trial, provided that his questioning in court was limited to two 90-minute sessions per day.
Mr Demjanjuk's family have said he is too frail to stand trial because he suffers from kidney disease, cancer and arthritis. In May, he was admitted to hospital for three days after developing gout.
The BBC's Steve Rosenberg in Berlin says it is unclear when the trial will begin, but it could be as early as this autumn.
Efraim Zuroff, the top Nazi-hunter at the Simon Wiesenthal Centre, which considers Mr Demjanjuk the world's most-wanted suspected Nazi war criminal, welcomed the move by German prosecutors.
"This is obviously an important step forward," he told the Associated Press. "We hope that the trial itself will be expedited so that justice will be achieved and he can be given the appropriate punishment."
"The effort to bring Demjanjuk to justice sends a very powerful message that the passage of time in no way diminishes the guilt of the perpetrator."
Mr Demjanjuk arrived in the US in 1952 as a refugee, settling in Cleveland, Ohio, where he worked in the car industry.
DEMJANJUK CASE TIMELINE
1952: Gains entry into the US, claiming he spent most of the war as a German prisoner
1977: First charged with war crimes, accused of being "Ivan the Terrible"
1981: Stripped of US citizenship
1986: Extradited to Israel
1993: Israeli Supreme Court overturns conviction, ruling that he is not Ivan the Terrible
2002: Loses US citizenship after a judge said there was proof he worked at Nazi camps
2005: A judge rules in favour of deportation to his native Ukraine
2009: Germany issues an arrest warrant for him; deported by US; formally charged with 27,900 counts of accessory to murder
In 1988 he was sentenced to death in Israel for crimes against humanity after Holocaust survivors identified him as the notorious "Ivan the Terrible", a guard at the Treblinka death camp.
But Israel's highest court later overturned his sentence, after documents from the former Soviet Union indicated that "Ivan the Terrible" had probably been a different man.
Mr Demjanjuk returned to the US, but in 2002 had his US citizenship stripped because of his failure to disclose his work at Nazi camps when he first arrived as a refugee.
In 2005, a US immigration judge ruled that he could be deported to Germany, Poland or Ukraine.
And in March 2009, prosecutors in Munich issued a warrant for his arrest, accusing him of being an accessory in the deaths of Jews.
They said they had documents proving his Nazi background, including an SS identity card which showed he had been a guard at Sobibor between March and September 1943, and many witness testimonies.