According to this press release, it’s the first time such a mass has been celebrated at America’s largest Catholic Church in nearly half a century:

The Paulus Institute announced today that on Saturday, April 24, 2010, at 1 p.m., the fifth anniversary of inauguration of Pope Benedict XVI will be commemorated in the Great Upper Church of the Basilica of the National Shrine of the Immaculate Conception, Washington DC, by a Pontifical Solemn High Mass in the “Extraordinary form”–commonly known as the “Traditional Latin Mass” or “Tridentine Mass”–celebrated by the Vatican prelate Darío Cardinal Castrillón Hoyos of Colombia.

This will be the first such Mass said at the Shrine’s High Altar in nearly 45 years. All Catholics are invited, many of whom may never have another opportunity to attend such a Mass. Cardinal Castrillón is the President Emeritus of the Vatican’s Pontifical Commission Ecclesia Dei (Church of God), where he assisted Pope John Paul II and Pope Benedict XVI in facilitating this Mass.

There’s more at the link.