"We are gathered here to remember and honour the youth who left us after the terror attack in Oslo," the head of Sweden's young Social Democrats (SSU) Jytte Guteland told a packed auditorium in central Stockholm.
"They were young just like us, they were politically involved just like us, they shared our values, they died young... We want the families to know their pain is shared, and that it is shared far beyond the nation's borders," she said.
On July 22, Anders Behring Breivik opened fire on the island of Utøya and killed 69 people, most of them teeenagers, who were attending a summer retreat run by the Norwegian Labour Party's youth wing (AUF).
The gunman described the attack as a "cruel" but "necessary" as part of his campaign against Muslim immigration to western Europe.
"We are gathered to show our sympathy to our sister organisation AUF," Guteland told the crowd of around 500 members between the ages of 13 and 30.
"No one should be afraid to stand up for their opinions, no one should be afraid to gather to change the world," she said, encouraging the delegates to carry on with their political involvement.
Her speech ended with a minute of silence.
Guteland had told AFP last week SSU was always in contact with police for large events and would not say if extra measures were taking following the massacre on Utøya.
On Tuesday, a metal detector stood at the entrance of the congress hall and security guards checked delegates' bags. Two policemen were seen in the area.
Joel Harde, a 22-year-old student who had travelled from the southwestern city of Gothenburg for the congress, said he had not been afraid to come, and that the attacks on Utøya had strengthened his political commitment.
"I feel we can do even more to disseminate our political views, our values," said the tall blond young man, wearing an "SSU Göteborg" t-shirt.
"It's very emotional. A lot of us had friends who were there," he told AFP, adding: "All of those I knew personally survived ... but a lot of my friends had friends who were murdered and that is horrible."
Harde acknowledged he fought back tears when former Social Democrat leader Mona Sahlin described her own memories of attending a Labour Party summer camp on the island where the massacre took place.
She described her 19-year-old self on Utøya, laughing and vowing a lifetime of friendship with "a blond girl with huge glasses and a dark-haired young man with beautiful eyes."
The blond girl, she said, was Anna Lindh, who was murdered in 2003 while serving as Sweden's foreign minister, and the dark-haired 17-year-old was Jens Stoltenberg, now Norway's prime minister.
After Sahlin's speech, former SSU leaders gathered on stage and lit candles.