The etiology of acute encephalitis was evaluated in a retrospective study of 170 children (98 boys and 72 girls) ages 1 month to 15 years, who were hospitalized during a 13-year period from 1979 to 1991. The etiology was confirmed or considered very probable in 68% of cases. The identified etiologic agents included Central European tick-borne encephalitis virus (28.8%), varicella-zoster virus (17.0%), herpes simplex (10.0%), rubella (2.9%), mumps (2.3%), measles virus, Chlamydia psittaci (1.1%) and some other agents found in individual cases. The etiology remained unknown in 54 children (31.7%). Forty-two patients had encephalitis with focal neurologic signs. The most common confirmed or presumptive infective agent in those cases was herpes simplex virus (40.4%), followed by rubella (7.1%), Central European tick-borne encephalitis virus (4.7%) and some other agents identified in individual cases. The etiology remained unknown in 15 (36%) children with focal encephalitis.