Between 1937 and 1986, Australian Indigenous people diagnosed with Hansen's disease (leprosy) were compulsorily isolated under the care of Catholic religious nursing Sisters in remote leprosaria across the north of the continent. This thesis explores the forces that gave rise to and maintained this policy; the underlying ideals and anxieties; and the ways the policy was executed across the four institutions that form the focus of the study: Derby (WA), Fantome Island (QLD), and Channel Island and East Arm (both NT). Missionary archival documents, oral histories and publications are used to examine the lives, work and traditions of the Sisters and other influential Catholic missionaries. Government records also reveal medical and social objectives implicit in the founding, staffing and ongoing operations of the institutions. Comparisons are made with management strategies for white Hansen's disease patients in Australia to unravel prevailing conceptions about the separate categories of race and disease. The Indigenous leprosaria derived from the Commonwealth government's interwar vision of a healthy White Australia, and the supervision and treatment of the inmates was considered a necessary corollary to this initiative. Catholic women religious were uniquely positioned for this role, being prepared for the incumbent risks, and having the requisite nursing and midwifery qualifications, resulting from a current upsurge in Catholic missionary activity in northern Australia. The Sisters expanded their nursing duties to encompass the holistic care of their patients and to educate them in Western skills, culture and morality. They ushered in the more intensive participation of Catholic Brothers and priests in evangelising the patients. In many ways the Catholic project aligned with government objectives for the social assimilation of the Indigenous population, but in the leprosarium, the object of such efforts was that ‘civilised’ and ‘Christianised’ residents would comply stoically with their enforced detention. Prescribed activities, whether hard work or leisure, were to keep patients occupied, diffusing their yearnings for home, and offering a gentler alternative to more punitive controlling measures. In later years, the Sisters became modern therapists, and agitators for better conditions and less stringent discharge criteria, thus more effectively helping patients regain their health and independence.