De Quincey's ‘Confessions of an English Opium-Eater’ (1821) and Berlioz's Symphonie Fantastique (1830) both take an unusual form in which seemingly digressive wanderings coalesce around an obsessively repeated motif: in both cases, an idealized young woman whose evasive near-presence is continually suggested through minimally varied repetitions of formal elements the artist associates with her. Although others have noted similarities between the two works – chiefly that both foreground a young artist-protagonist's opium visions – the works' structural parallels have been little discussed. This essay argues that an analysis of the commonalities between these strikingly similar formal innovations supplements previous arguments in significant ways, illuminating the oeuvres of both Berlioz and De Quincey as well as aspects of Romantic formal experimentation in general.