The Oslo bombing and Utoya island shooting killed a total of 77 people last month.
The ceremony comes a day after survivors returned for the first time to the site of the island shooting, where
the gunman killed 69 people. He also bombed the Oslo government buildings on the same day, killing eight more people.
Most of the victims were at a political summer camp held by the youth wing of the governing Labour Party at the time of the July 22 shooting attack.
Most survivors made it out alive by hiding among rocks or diving into the chilly waters around the island.
Before the survivors' visit, relatives of those killed traveled to the island Friday for the first time to see where their loved ones spent their final moments.
Many lit candles and left flowers in makeshift shrines.
The suspect in both attacks, Anders Breivik, was ordered held in isolation for four more weeks Friday after appearing before a judge in Oslo.
If removed from isolation, there's danger that he will tamper with evidence and hinder the police investigation, the judge said.
Breivik, 32, had told the court that being held in isolation is "boring, monotonous and a sadistic method of torture," the judge said.
The suspect admitted the attacks, a judge and his lawyer say, but has pleaded not guilty in court.