This article explores two very different forms in which immoral conduct was problematized over the course of the 19th century. It does this by contrasting the sexual purity politics of the Vice Society and the medicalization of morality as `moral insanity'. Early in the century the Vice Society promoted coercive legislation with the aim of `suppressing vice'. From mid-century, moral insanity theories sought to grapple with vice by disaggregating `moral' from other forms of insanity. These two movements had quite distinct (...) and incompatible lines of development; and they never overtly engaged with each other. The article makes its key argument by demonstrating the way in which such dissimilar trajectories came together towards the end of the century in the `moral hygiene' movement, mobilizing discourses of `degeneration' (and `feeblemindedness') with projects promoting sexual purity. (shrink)