The statistic which found its way into all of the headlines was Kinsey's assertion that 10 per cent of all American adult males were "more or less exclusively homosexual", including 4 per cent who were "exclusively homosexual throughout their lives, after the onset of adolescence".
The accuracy of those numbers has been challenged repeatedly since they were published, and the debate heated up again last year, when James H. Jones published a massive new biography of Kinsey. Jones broke the researcher's most carefully guarded secret - the fact that he was having sex with men throughout his marriage - and suggested (not very convincingly) that this behaviour might have affected Kinsey's scientific methods.
What made Kinsey's work revolutionary was his assertion that scientists had to divorce their judgements about sexuality from the "ancient religious codes" which were "the prime source of the attitudes, the ideas, the ideals, and the rationalisations by which most individuals pattern their sexual lives".
By adopting a disinterested tone and divorcing all of his judgments from the traditional Judaeo-Christian influences, Kinsey eventually made it possible for millions of people to think about sex very differently. His book was another crucial step in the evolution which had begun a century earlier with Darwin: the gradual triumph of science over religion which ultimately made gay liberation possible.
In 1948, the legions of psychiatrists who had made handsome livings by trying to convert homosexuals into heterosexuals were oblivious to Kinsey's achievement. They were apoplectic over Kinsey's findings - even though their progenitor, Sigmund Freud, had written in 1937 that while "homosexuality is assuredly no advantage", it was also "nothing to be ashamed of, no vice, no degradation [and] it cannot be classified as an illness".
Religious leaders and academics were even harsher: Henry Van Dusen, who headed Manhattan's Union Theological Seminary, called the report's statistics evidence of a "degradation in American morality approximating the worst decadence of the Roman era", while the President of Princeton University compared the report to "the work of small boys writing dirty words on fences".
But Kinsey's conclusions would have a much more lasting effect than the words of his critics. He had begun a process that would eventually produce a dramatic change in the way the American establishment thought about homosexuality.
Kinsey wrote that, considering the number of homosexuals he had uncovered, it would be "difficult to maintain the view that psychosexual reactions between individuals of the same sex are rare and therefore abnormal or unnatural, or even that they constitute within themselves evidence of neuroses or even psychoses". That was the conclusion which enraged psychiatrists most of all. But exactly 25 years later, it became the official position of the American Psychiatric Association, when it removed homosexuality from its official list of mental disorders in 1973. For gay Americans, that action was just as revolutionary as the Declaration of Independence had been for the colonies
Charles Kaiser is the author of `The Gay Metropolis: 1940-1996' (Weidenfeld & Nicolson, pounds 20)