The British Nationality Act 1948 conferred citizenship on Commonwealth subjects, granting them the right to settle in Britain. Hundreds of thousands of New Commonwealth migrants made use of the Act. Almost immediately, opponents began criticizing the health impacts of immigration, focusing on diseases like syphilis and gonorrhoea. More than any other migrant group, Black British men from the Caribbean became implicated in debates over venereal disease. This article explores how health workers and journalists used health data in ways that reinforced racial stereotypes, fed white prejudices and presented Black men as the most significant sexual health threat in postwar Britain.