The nature and extent of EEG changes in 114 patients with tick-borne encephalitis were reported. The diagnosis was confirmed by the clinical picture, as well as the pathological increase in cells in the liquor and serologically by positive Ig-M titres. EEG findings were compared in patients with or without involvement of the brain. The EEG revealed pathological results in 76 patients, whereby the dominant pathological change was frequently occurring synchronous bursts of generalized slow bilateral waves. 12 patients with involvement of the brain all showed pathological EEG changes, a much higher rate than in the remaining patients and these findings were also more marked. However, 64 patients with clinical evidence of meningitic involvement showed pathological EEG changes, too.