This special issue of Memorias do Instituto Oswaldo Cruz focuses on leprosy (Hansen's disease or hanseniase in Portuguese). It is fitting that this issue is being published on the 100th anniversary of the death of Gerhard Henrik Armauer Hansen, the Norwegian physician who first identified the bacterium, Mycobacterium leprae, as the causative agent of this disease in 1873. Although Hansen's disease has been all but eliminated in this country, it is still a major health problem in many parts of the world. The latest statistics reported by the World Health Organization showed that worldwide new case detection was 228,474 in 2010. In Brazil, there were 34,894 new cases diagnosed, with 2,241 reported in children (6.4%), indicating that there are still areas where leprosy is clearly a health problem. Although it is true that Brazil remains one of the last remaining countries yet to reach the goal of less than one new case per 10,000 population, the degree to which the public primary health care service and Brazilian leprologists are working towards detecting and treating all cases is a testament to the strength of the program.