As the First World War ‘ended’, one of its most devastating legacies continued. The global spread of the Spanish influenza virus in 1918–19 had been facilitated by the mass movement of troops and other personnel around the world. This pandemic has traditionally been relegated to the footnotes of the First World War, and yet it killed more than both world wars combined. The most virulent wave of the pandemic struck in the autumn of 1918 and, in many belligerent countries, coincided with the signing of the Armistice. Across the British Empire, the dynamics between the pandemic and the end of the war varied between different imperial spaces. In Australia, a partially successful national quarantine led to international acclaim, and augmented the health-focused aspects of its developing national self-image. In other imperial spaces, however, the pandemic presented a challenge to national self-image. New Zealand failed to control the pandemic either within or outside of its shores, and its role as an imperial outpost in the South Pacific was jeopardised by its failure to enforce quarantine in Western Samoa during the outbreak. Yet, in indigenous imperial spaces the pandemic could facilitate change in the aftermath of the war. Indigenous Samoans, for example, utilised the pandemic to further the cause of their nascent national independence movement. Such examples illustrate how the Spanish flu pandemic provided unique opportunities and challenges for British imperial hegemony in the aftermath of the First World War.