Bernard Herrmann’s music for Hitchcock’s Psycho plays a crucial role in implementing the relentless move towards mayhem and madness which is characteristic of this film, as well as in creating distorted reflections between sanity and madness. In this article, I claim that the former aspect is expressed by a gradual move from tonal towards “mistuned” and then atonal harmonic objects, while the distorted mirror relationship is suggested by a number of subtle correspondences (both similarities and differences) between cues associated with Marion and cues associated with Norman. My analysis rests on both intratextual and intertextual factors. While I reveal the former through a close analysis of the film score in relation to the narrative, I discuss the latter in terms of Herrmann’s general approach to film music, the conventions of horror film scoring, and the special linkage between modernist music and madness in concert music, opera and cinema.