 Vlaar was part of the Netherlands U21 on the 2006 UEFA European Under-21 Football Championship, where the Dutch side claimed the trophy for the first time in history.Besides the group match against Denmark U21 (1–1), Vlaar played in every match on the tournament.Jong Oranje started and finished their campaign against Ukraine U21, going out on a high with a 3–0 win in the final, after surprisingly losing their opening game to the Ukrainian team.