This study examines the reception of the controversial science of eugenics in Catalan and Valencian anarchist reviews in the early twentieth century, setting anarchist discourse on sexuality, theories of degeneration, inheritance and disease in the context of anarchism’s own ideological framework, European sexology and eugenics itself. Drawing on a detailed analysis of the reviews Salud y Fuerza, Generacion Consciente and Estudios, the author suggests that some anarchists’ acceptance of eugenic science was predicated upon their enthusiasm for science as ‘objective knowledge’ and ‘scientia’ as a form of cultural ascendancy vital to their revolutionary project. Anarchist eugenics, however, as articulated in these reviews, was not stable and shifted focus and scientific rationale over time and as new ideas came to the fore. The author shows how far the social and ideological concerns of anarchists constructed their form of eugenics and how eugenic science in turn helped to construct a form of anarchism which sought to incorporate sexological science into what anarchists believed was a radical sexual project for the age.