This article is a discussion of Sigmund Freud’s note on ‘The Perversions in General’ from the 1905 edition of his Three Essays on the Theory of Sexuality. To summarise its argument, the article proposes that what Freud calls ‘perversion’ is itself to be properly understood as a form of sexual generalisation. It goes on to contend that Freudian perversion thus has larger implications for our understanding of the new sciences of sexual generalisation (sexology, psychoanalysis, structuralism, genealogy) that are beginning to emerge from the end of the nineteenth century onwards. If perverse sexuality is arguably the defining libidinal object of Krafft-Ebing’s sexual taxonomy, for example, the article argues that perversion is already in itself a form of perverse sexual taxonomy. In conclusion, the article argues that Freud’s perversion is consequently a form of structural ‘dis-content’ that cannot be contained within the modern sciences of sex which extend from Krafft-Ebing’s sexology to Foucault’s history of sexuality.