The APA decision December 1973: declassification of homosexuality as an illness, Charles Kaiser argues, was the gay movement's most revolutionary moment. (Bold beginnings).

The best day of the 20th century for every lesbian and gay man in America was December 15, 1973: the day the board of the American Psychiatric Association voted 13-0 to remove homosexuality from its official list of psychiatric disorders.

It was the front page story in The New York Times (and almost every other major newspaper) at the time, and it remains the most important victory of the modern gay rights movement, which was then slightly more than four years old.

The triumph was a tribute to the diligence, intelligence, and furious determination of Frank Kameny, a cofounder with Jack Nichols of the Washington, D.C., branch of the Mattachine Society and one of the most important gay leaders of all time. More than a decade before the APA acted, Kameny identified homosexuality's classification as a mental illness as the major stumbling block for gay rights because "an attribution of mental illness in our culture is devastating."

When Kameny studied the psychiatric literature, he was "appalled." He told me that everything he found there was "sloppy, slovenly, slipshod, sleazy science--social and cultural and the theological value judgments, cloaked and camouflaged in the language of science, without the substance of science. There was just nothing there.... It was garbage in, garbage out."

In short, after centuries of religious persecution, gay people had suffered throughout the 20th century from outrageous medical malpractice: the psychiatric notion that the only healthy gay person was the one who wanted to be straight.

In 1970, Kameny convinced the Gay Activists Alliance to join him in his campaign to overturn the APA's policy, and only three years later they were successful.

For gay people who came of age after the 1970s, it is almost impossible to imagine what it had been like to live in an era when every official body (as well as most liberal lobbying groups, including the American Civil Liberties Union) classified your orientation as an illness or a crime. As Judd Marmor, one of the APA officers who engineered the change in the association's official doctrine, told me, the board of trustees concluded there was "no reason why ... a gay man or woman could not be just as healthy, just as effective, just as law abiding, and just as capable of functioning as any heterosexual." That was an entirely revolutionary notion in 1973, and without its formal articulation none of the progress of the next three decades would have been possible.

Kaiser is the author of the books 1968 in America and The Gay Metropolis.