The Six Nations Under 20s Championship is an international rugby union tournament for the under-20 men's teams of the national unions making up the Six Nations Championship and is organised under the same format.

Originally the tournament was in an under-21 format but changed after four editions to under-20s in 2008. England were the inaugural winners and they have gone on to be the tournament's most successful team, winning ten of the twenty-one titles up to 2025 (the 2020 competition having been abandoned during the Covid pandemic), while four of the six teams involved have won the competition at some point.

The tournament is played annually during February and March on the same weekends as the senior men's Six Nations. The competition retains from its senior equivalent the concepts of both the Grand Slam, Triple Crown and the Wooden Spoon.

Winners Six Nations Under 21s Championship Year Winner Grand Slam Triple Crown Ref. 2004 2005 2006 2007 Six Nations Under 20s Championship Year Winner Grand Slam Triple Crown Ref. 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Cancelled 2021 2022 2023 2024 2025 2026

Statistics   Tournaments 22 22 22 22 22 22 Wins Under-21 Championship 2 1 1 Under-20 Championship 8 5 4 1 Overall 10 5 5 2 Grand Slams Under-21 Championship 2 1 1 Under-20 Championship 4 2 3 1 Overall 6 2 4 2 Triple Crowns Under-21 Championship 2 1 1 Under-20 Championship 6 6 1 Overall 8 7 2 Wooden Spoons Under-21 Championship 1 2 1 Under-20 Championship 1 7 8 1 Overall 2 9 9 2

References