World Down Syndrome Day is marked each year on March 21, beginning in 2007. The 21st day of March was selected to signify the uniqueness of the triplication of the 21st chromosome which causes Down syndrome.

For World Down Syndrome Day, on 21 March 2025, Down Syndrome International is calling on all Governments to Improve Our Support Systems. Each year for World Down Syndrome Day, our team develops a message we ask supporters to share. This is something that we believe needs a lot of attention all around the world.