The subject of this paper is the medical service of the Anglo-Iranian (formerly Anglo-Persian) Oil Company (AIOC), which operated in southwest Iran from 1909 to 1953. Through an investigation of the AIOC’s network of hospitals and dispensaries, the political role of its doctors, and its sanitary efforts and public health campaigns, I argue that the AIOC’s introduction of modern medical practices and institutions to southern Iran constituted a case of colonial medicine; in other words, it served as an instrument of empire and a colonizing cultural force. Relying on AIOC medical reports, correspondences between company doctors, and other medical records available at the BP (British Petroleum) Archive, as well as British India Office and Foreign Office documents relating to health and sanitation in the Persian Gulf region, my paper addresses the theme of colonial medicine in three principal ways. First, challenging triumphalist narratives of medical development, it sheds light on the violence that accompanied the AIOC’s sanitary measures; the company’s efforts to combat disease often involved coercion and the dispossession and displacement of local peoples. Second, it highlights the role of the medical knowledge produced and relied upon by AIOC doctors in reinforcing notions of racial hierarchy and marking colonial difference. Third, it examines the disciplinary component of AIOC medical practices, framing them as part of a broader effort by the oil company to transform the local population into modern subjects who would facilitate rather than hinder the smooth operation of a major industrial enterprise. In addition, this paper elucidates the relationship between public health and sovereignty in Iran by arguing that the Iranian state’s 1928 repudiation of British and AIOC control over quarantine responsibilities in southern Iran was indicative of a growing sentiment within Iran that the ability to protect the country’s borders and bodies from disease was a source of political authority and legitimacy. Drawing on recent culturally grounded approaches to the study of empire, my paper contributes to the history of both modern Iran and the British empire by demonstrating that imperialism in Iran was not confined to economic exploitation or overt political domination. Rather, British imperial authority in Iran was also premised on the articulation of modern medical knowledge and the inculcation of new medical practices. By treating the AIOC as an imperial institution, this study reveals the key role that informal imperialism played in the unfolding of modernity in Iran.