From 1997 to 2000, complete necropsy and histopathologic investigations were performed on 157 free-ranging European brown hares (Lepus europaeus) found dead throughout Switzerland. Organ samples of all these individuals (157 livers and 107 spleens available) were tested for European brown hare syndrome virus (EBHSV)-antigen by enzyme-linked immunosorbent assay (ELISA) test kit. Furthermore, 60 additional blood samples were tested for antibodies against EBHSV by ELISA. In addition, liver samples of 87 free-ranging mountain hares (Lepus timidus) hunted in 1996 were tested for EBHSV-antigen. In two European brown hares from southern Switzerland lesions suggestive of changes induced by EBHSV were present, and high titers of EBHSV-antigen were detected in both liver and spleen samples of these animals. Based on negative staining electron microscopy investigations of liver and spleen homogenates, we observed calicivirus in one antigen-positive hare. Low EBHSV-antigen titers were found in three additional European brown hares from central and western Switzerland, but EBHS-lesions were absent. Antibodies against EBHSV were not detected in any of the sera of European brown hares, and EBHSV-antigen was not found in the samples of mountain hares. This is the first report of EBHS in European brown hares from Switzerland.