Poland's president has promised to restore citizenship to thousands of Jews who were expelled from the country by the communists in 1968. ( BBC )
Lech Kaczynski described the decision to kick out about 15,000 Jews - many Holocaust survivors - as "shameful".
The purge followed nationwide student protests that began after a decision to close down a patriotic play.
People of Jewish origin were blamed, stripped of Polish citizenship and ordered out of the country.
Police violently broke up a student demonstration at Warsaw University 40 years ago.
It had been caused by the communist authorities' decision to close down a patriotic play by Poland's national poet, Adam Mickiewicz.
The protests quickly spread across the country before being crushed with considerable violence.
Many of the students and professors were of Jewish origin and the communist party used that fact to purge Jews from public life.
An estimated 15,000 people - half the country's Jewish population - were given a one-way ticket out of the country and stripped of their citizenship.
Among those attending Saturday's anniversary ceremony was Michal Sobelman, one of those forced out in 1968.
"We left because we couldn't be Poles and we couldn't live here as Jews," Mr Sobelman said.
"The Poland of those times did not want us," he said.
"But with our suitcases we took a little bit of Poland that was with us for 40 years. Today, in some symbolic way, we return it to end this sad chapter," Mr Sobelman said.
Mr Kaczynski said the campaign was an enormous loss for Poland.
"It was a very bad and shameful time," he said.
"The nation lost its reputation for many years and the damage has still not be completely repaired.
"An even greater loss was that thousands of often very talented, ambitious and entrepreneurial people had to leave our country."
The president went on to promise to make up for the communist-era decision by restoring Polish citizenship to those who wanted it.
"I am ready, without any formalities or even requests... to return citizenship to everyone from those times who will want it," Mr Kaczynski said at a ceremony in Warsaw at one of the train stations where thousands had boarded to leave.
"I treat this as my personal contribution to reversing the consequences of those sad, shameful events. Never more."