This article documents Joseph Lister’s reluctance to publish numerical material and aims at explaining his skeptical view about statistics through an investigation of his approach in its historical context. In this context, statistics was only one kind of evidence used in surgery, along with case histories and experimental results from the laboratory. They represent different “ways of knowing,” anchored in different social, conceptual, and practical contexts. The account looks at Lister’s approach to wound disease and analyzes how this relates to his attitude toward different types of evidence about surgical outcomes. For this, it also examines his contemporaries’ approaches to fighting wound disease as well as their evaluation of different kinds of evidence. This article is a contribution to the history of Lister’s antisepsis, but also to the history of the production and use of therapeutic knowledge in nineteenth- and early twentieth-century surgery more generally.