From October 1st through the 30th, former players will be able to return to the game for free, mirroring previous Return to Britannia events.
There's a lot to celebrate in UO these days above and beyond its birthday. The game recently implemented its Publish 86 with the vice vs. virtue system, added more sea adventures, and is working on a new UI for the enhanced client. You can check out video of the 17th anniversary festivities after the break.
[Update: Players are reporting that the Return to Britannia campaign is not resurrecting very old accounts.]