In an 8-year-old girl a seizure occurred, lasting 45 min with loss of consciousness and deviation of the eyes, 2 days after the onset of mumps. Next day the EEG showed bilateral, synchronized, continuous 2.5-3.5 c/sec spike-wave discharges, more prominent over the posterior regions. The abnormality was suppressed on eye opening and replaced by delta activity and short duration spike-wave paroxysms. Mental activity, hyperventilation, and photic stimulation did not change the pattern. The same EEG pattern persisted during daytime sleep. This picture has lasted for 17 months without any associated epileptic manifestations or behavioural disturbances. Psychometric tests and CAT scan were normal.