The Leishmania/HIV co-infection has emerged as a result of the increasing overlap between leishmaniasis (mainly visceral, more rarely cutaneous) and AIDS, which is due to the spread of the AIDS pandemic to rural areas and that of visceral leishmaniasis to suburban areas. Cases of co-infection have so far been reported from 33 countries around the world, most of the cases have been notified in south-western Europe. 1,627 cases have been notified from Spain, France, Italy and Portugal. While Leishmania/HIV co-infection is increasing in eastern Africa, cases of co-infection are expected to diminish in South-western Europe due to the new highly active anti-retroviral therapy (HAART). In 1998, a world wide WHO/UNAIDS surveillance network was established, which now includes 28 member institutions. In south-western Europe, the surveillance system based on 16 institutions is now well established. The systematic use of standardized and recently computerized case-report forms, the central international registry at WHO headquarters, and finally the use of a geographic information system (GIS) for mapping and monitoring co-infections have improved the overall quality of epidemiological data gathering. All member institutions of the network report to WHO on an annual basis. World wide information is analysed and periodically disseminated through international publications. The GIS integrates epidemiological and demographic data sets and allows for the mapping of co-infection cases down to locality level. The system can be used to easily visualise and analyse the spatial distribution of co-infection cases and to permit monitoring of the evolution of the distribution of the cases over time. The risk of co-infected patients, as carriers of Leishmania in the blood, to be a source of infection for the sandfly, has been recently confirmed. Moreover intravenous drug users also transmit the disease through the sharing of needles.