The EEG findings in 105 hydrocephalic children with proven ventriculomegaly and increased intracranial pressure are reported prior to initial shunt treatment in the Department of Pediatrics, University of Oulu, Finland. Abnormal EEGs were seen in 98%. Paroxysmal slow wave activity, generalized or posterior, was present in 37 (35%) recordings and focal slow waves in 28 (27%) patients. Spike or sharp wave activity was recorded focally or generally in 45 (43%). The prevalence of spikes and sharp waves became less with increasing age and only generalized spikes occurred after seven years of age. The etiologies of the hydrocephalus were perinatal hemorrhage (20), infection (10), tumor (11), and malformations (64). Of 45 patients studied between one month and one year of age five had hypsarrhythmia. 
COMMENT. It is important to study the electroencephalogram of infants with hydrocephalus prior to shunting so that effects of increased intracranial pressure and malformations can be distinguished from those secondary to the shunt and possible infection. Spikes and sharp waves in the EEG of hydrocephalics are predictive of the prognosis and the probable occurrence of epilepsy.