The so called slit-ventricle syndrome appears as a potential complication of the CSF derivations, whatever their types. It consists of repetitive episodes of elevated intracranial pressure, associated with collapsed ventricles as demonstrated by CT scan. Clinical symptoms happen after several months or years during which the derivation worked well, and then get more and more frequent. Between the episodes, the only statement one can do is the slow re-filling of the pump after it has been depressed with finger. The valveless lumbo-peritoneal derivations, and the ventriculo-atrial or ventriculo-peritoneal derivations using a low-pressure valve, are most often found in patients with the slit-ventricle syndrome. This suggests that overdrainage of the CSF is likely to be the main cause of this syndrome. Possible managements comprise: changing the valve, for an other one with a higher opening pressure,--adding to the derivation an antisyphon device, and making a subtemporal decompression.