In the spring of 1995, the largest outbreak of hemorrhagic fever with renal syndrome (HFRS) so far was recorded in Croatia. There were 125 patients reported to the National Croatian Institute of Public Health, Department of Epidemiology. The disease occurred simultaneously in several localities, some of them close to the previously known natural foci (Mala Kapela, western Slavonia); the focus on Dinara was newly discovered. War circumstances in Croatia were closely related to this outbreak. There were 50 patients hospitalized in the University Hospital of Infectious Diseases in Zagreb; 5 of them were civilians from Zagreb area and 45 soldiers (Mala Kapela 33, Dinara 7, western Slavonia 5). In all patients the disease was serologically proven (in 6 by indirect immunofluorescence method and in 44 by ELISA-test). Both previously known types of viruses--Hantaan and Puumala were diagnosed in each locality. In general, the illness was more severe in patients with Hantaan virus infection. Two patients died, the illness was severe in 25, moderately severe in 11 and mild in 12 patients. For the first time inflammatory lung changes were recorded in 13 out of 37 (35.1%) patients who were examined by X-ray in the early stage of the disease.