The Kim Il Sung Socialist Youth League plays a major part in North Korea's social system.
Young people from the ages of 14 to 30 are expected to join and take part in activities ranging from study sessions to helping out in major construction projects.
North Korea says the youth league has five million members.
Pyongyang's May Day Stadium, which has a capacity of 150,000, was almost full tonight, and the crowd stood and cheered as Kim Jong Un walked in.
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Fireworks burst above the stadium at the show's climax.
North Korean state media did not immediately report on what took place at the 9th Congress of the youth league, which ran Friday through today.
Foreign media were not allowed in.
The 8th Congress was held in February 1993.