The best therapeutic management for infantile hydrocephalus is not always obvious. Traditionally, shunt insertion has been performed when CSF dynamics have been considered abnormal. However, in cases of noncommunicating hydrocephalus endoscopic III ventriculostomy (ETV) has become a well-established treatment modality, but despite clinical and radiological information clinical improvement is not obtained in all cases. A reliable preoperative investigative procedure helping to select hydrocephalic children for ETV, shunt insertion or no operation, is urgently needed. We report three cases of infantile hydrocephalus, in which our operative management was guided by the results of cerebrospinal (CSF) infusion tests. With a lumbar infusion test we assessed the CSF resorption capacity, and thus whether shunting was indicated. Comparing the results with those of an intraventricular infusion test, we assessed the presence of any structural blockage of the CSF circulation between the ventricles and the subarachnoid compartment, which would indicate a possible effect of an ETV. Performance of both a lumbar infusion test and a subsequent intraventricular infusion test in hydrocephalic children seems to provide valuable information for the decision-making on surgery.