The modern history of the regulation of entry of non-citizens, the emergence of the nation-state in the nineteenth and twentieth centuries, and the history of public health, are all receiving increasing historical attention. This article explores the micro-politics of the tuberculosis screening debate in Britain between 1950 and 1965. It focuses on a key question. Given the pressure to adopt a policy of compulsory chest X-rays at ports of entry, why did the United Kingdom adopt the port of arrival system in which the major element comprised the forwarding of addresses of arriving migrants to public health doctors in intended districts of residence? The article explores the three main options available to policy-makers—screening before departure; screening on entry and screening after arrival. It also traces legal, economic, political, epidemiological and pragmatic arguments and debates. The article contributes to contemporary discussion about tuberculosis screening and the port of arrival system in the UK, and draws out broader themes to do with nationalism, migration and public health.