In 1928 there was an estimated 1.2 million “out” homosexual men living in Germany. As Adolph Hitler rose in power, gay organizations were banned and scholarly books regarding homosexuality were burned. Between 1933 and the start of WWII, these homosexual men were recorded in “pink lists”. Eventually 100,000 of these men were sent to concentration camps, where an estimated 55,000 were executed.
The pink triangle (now a symbol of Gay Pride) was placed on the prisoners to mark that they were homosexuals.
After the war the homosexuals were left out of the Holocaust picture, until the 1980s. And in 2002 the German government apologized officially to the gay community.
In 2008 a Holocaust Memorial for Gays was unveiled in Berlin. To see photos of the memorial: http://www.ilga-europe.org/
Link to the film documenting the stories of gay Holocaust survivors: http://www.petertatchell.net/history/survivors.htm
Video documenting gays in concentration camps (courtesy of YouTube): http://www.youtube.com/watch?v=OUWzlsA7qDk&feature=related