External hydrocephalus means abnormal fluid accumulation in the subarachnoid space under increased pressure with no or slight widening of the ventricles. 9 children were investigated because of pathologically increasing head circumference and abnormal transillumination. PEG and/or CT showed widened sulci frontally, parietally and interhemispherically but no widening of the ventricles. 7 patients were subjected to exploratory craniotomy which disclosed a deep arachnoid space. 2 patients were shunted. All follow-up CT examinations showed normal conditions. We suggest that infants with clinical signs of hydrocephalus and CT picture of external hydrocephalus should not be treated with shunt. The widening of the subarachnoidal space will normalize. The rate of headgrowth will also normalize.