World Down Syndrome Day is observed annually on March 21st to raise awareness about Down Syndrome, advocate for the rights, inclusion, and well-being of people with Down Syndrome, and to celebrate the potential and accomplishments of those with Down Syndrome.
 
Wearing mismatched socks on March 21st is a way to celebrate World Down Syndrome Day and raise awareness about the disability. The date 3/21 is symbolic because people with Down Syndrome have three copies of chromosome 21, instead of the usual two. The idea came from the observation that chromosomes look like socks in a karyotype, and the extra copy is represented by wearing an extra sock.