Most scholarship on Anglo-American missionaries in al-Mashriq focuses on ecclesiastical and educational endeavors during the nineteenth century, demonstrating how translation, printing technologies, and pedagogy transformed missions and society. However, less scholarly attention has been paid to the centerpiece of the mission encounter—medicine. This paper fills the gap in terms of period and institutional focus. It considers the evolution of Anglo-American missions during the twentieth century, concentrating on the development of missionary medicine and its relationship with Gazan society. I approach this topic by analyzing the Church Missionary Society (CMS) medical mission in Gaza (1882-1954). Support from British colonial officials, paired with technological innovations in medicine, allowed CMS missionaries to establish medical missions in Egypt, Palestine, and throughout the Ottoman Empire during the late-nineteenth century. Although missionary medicine, including its iteration in Gaza, relied on British colonial power, it forged a unique strategy for medical care differentiating it from colonial medicine. Informed by Gazan patient records and CMS periodicals, this paper defines missionary medicine as a distinct category of modern medicine; it then analyses how missionary medicine defined and engaged Gazan society. Missionary medicine in Gaza was neither parochial in practice nor universal in intention. It offered medical care to the entire population, yet limited medical pedagogy to Arab Christians. CMS missionaries divided their understanding of Gazan society into dichotomies: wealthy and impoverished, urban and rural, male and female, Muslim and Christian. Within each pair, the missionaries maintained a commitment toward serving the impoverished, rural, and female members of Gazan society, with the support of a Christian staff. Eventually, the immutable calculus of missionary medicine could not withstand a rapidly evolving Gazan society. The developing sociopolitical landscape in Gaza rendered this iteration of missionary medicine inoperative.