From the initial cholera pandemic that reached Japan in the 1820s up to the Sino-Japanese War in 1894-1895 the Japanese medical community conceptualized cholera in a number of ways that reflected both shifting understandings of the disease related to changes in medical knowledge, as well as a consistent perception that posited cholera as an outside illness. This paper offers a brief overview of the various disease classifications used to refer to cholera during the nineteenth century and focuses on the use of the term “Asiatic cholera” in Japanese medical writings in official government documents and medical journals. Prior to the 1880s Japanese practitioners of Western scientific medicine, here defined as a form of medical knowledge originating in Europe and shaped by institutions like medical schools, universities and research centers, viewed cholera within the dual framework of Asiatic cholera and kakuran. The disease category of Asiatic cholera originated in Western medical writings in the nineteenth century and referred to a deadly epidemic disease associated with Asia, while kakuran was a Japanese medical term that indicated a less pernicious enteric illness. In general Japan’s medical community used these two disease categories to differentiate between a dangerous foreign malaise and a milder Japanese illness. In 1883 German medical researcher Robert Koch demonstrated that cholera resulted from a microbial pathogen he called the cholera vibrio. His work was instrumental in laying the groundwork for Germ Theory, which was an understanding that linked the onset of a specific infectious illness to a specific microbial pathogen. The Japanese medical community’s broad embrace of Germ Theory should have brought an end to the epidemiological binary of Asiatic cholera and kakuran in favor of one disease, cholera. My research demonstrates that the continued use of Asiatic cholera in Japanese medical writings persisted, because conceptually it implied a clear distinction between Japan and the Asian continent.