The demography of both urban and rural South Africa is shaped by migration, with three unique patterns: labour-sending, labour-receiving and rural areas. This article explores the relationship between HIV risk and migration in South Africa. It identifies the urban informal settlements common in labour-receiving areas as key magnifiers of HIV risk, increasing the vulnerability of migrant workers in these townships. It examines the urban informal settlement, a unique social environment with distinctly high-risk behaviour dynamics, as a focal determinant of HIV. It pro- poses this framework as an extension of the migration – HIV dialectic beyond the traditionally uni- dimensional approach, to encompass a more contextualised discussion. This methodology, which uses the environment as an entry point to understanding behaviour and emphasises the importance of addressing the HIV–migration issue within a broader development perspective, has important implications for HIV programming in South Africa.