The largest secret Santa event involved 1,270 participants.
(It was organized by Boots UK Limited in Nottingham, UK, on December 18, 2008. Secret Santa is a tradition in which members of a group are randomly assigned other members to whom they anonymously give a gift. All the participants agree on a price limit and then they write their names on small pieces of paper and put them in an envelope. Each person then draws a name. The name drawn is the recipient of the gift. You'll usually find secret Santa events in workplaces, because it helps to limit the number of gifts people have to buy.)