Hemorrhagic fever with renal syndrome (HFRS) has been known from ancient times as a disease with many names, which raised great interest during the Korean war (1951-1954), occurring as a large epidemic (Korean hemorrhagic fever). Therefore, the subsequently discovered causative agent was named after the Hantaan River which runs along the 38th parallel and divides North Korea from South Korea. A similar disease was described in 1934 in Scandinavian countries (epidemic nephrosonephritis or nephropathy). During the Second World War, the disease was also registered as wartime nephritis in several European south-eastern countries. Since 1982, similar clinical manifestations of the disease, differently named in various parts of the world, have been assigned one unique name--hemorrhagic fever with renal syndrome, as recommended by the World Health Organization. In Croatia, the first patient with HFRS was diagnosed in 1952 and the paper describing the case was published in 1954 (Radosevic and Mohacek). Since then, the disease has been regularly occurring in our country, especially in sporadic form, with only two smaller epidemics recorded until 1995. The first epidemic with 14 forestry workers involved occurred in 1967 at the Plitvice Lakes, and the second with the same number of soldiers in 1989 around the Pieso-Airport near Zagreb. Simultaneously, in 1967 and 1989 two large-scale epidemics of HFRS occurred in Bosnia and Herzegovina with 144 cases each. Until the first large epidemic of HFRS in Croatia during the Croatian War in 1995, occurring at several localities (Mala Kapela, Dinara mountain, west Slavonia), it was considered that there were only several natural foci of the disease in Croatia (around Ogulin and Slunj, Plitvice Lakes, Zagreb surroundings). A total of 125 cases were reported to the Croatian National Institute of Public Health in 1995. Fifty patients, 45 of them soldiers, were hospitalized at Dr. Fran Mihaljević University Hospital for infectious Diseases in Zagreb. In the same year, the largest epidemic also occurred in Bosnia and Herzegovina with more than 300 cases. During the almost 50-year experience in HFRS surveillance, we have noticed two different clinical manifestations of the disease. The milder type of illness without hemorrhage is more common than the severe type with hemorrhages and extensive renal insufficiency. After the virus discovery and introduction of serologic testing, two causative agents have been detected during the 1970s and 1980s--Vranica and Fojnica, that were later serotyped as Puumala and Dobrava viruses.