Leprosy continues to be a disease of public health importance in Brazil and many other low and middle income countries. Not much is known about the social epidemiology of leprosy nor the effectiveness of social policies on this poverty-related disease. We propose a new way to investigate wich aspects of poverty increase the risk of leprosy, and how much Bolsa Familia ( a conditional cash transfer programme) introduced by the Brazilian government helped to decrease the risk of leprosy, reduced the risk of disability, and increased the proportion of cases of leprosy that completed treatment. We are going to do this by using data already collected for administrative purposes. The main database is "Cadastro Único para Programas Sociais" (CadÚnico), used for screening applications for social programmes, which contains data on a range of socioeconomic indicators for 100 million people. We will link this to two databases: of benefits received, and to notification of leprosy. This will be done protecting the identification of individual data with strict security measures approved by the ethical committee. The unprecedented size of this cohort will allow the investigation of effects of social conditions (education, income, housing, family structure, ethnicity, water supply, sanitation) and of impact of interventions (income received, duration of support) on different aspects of leprosy in subpopulations defined by type of disease, age, geography, income, gender, housing, etc.. The project will produce evidence of the impact of social interventions and social deprivation on leprosy. The study will advance our understanding of leprosy and will strengthen the case for implementation of social interventions- in addition to biomedical interventions-to promote effective control of leprosy and pave the way for evaluation of impact on other poverty related diseases.