Implantable device for the treatment of the hydrocephalus syndrome in a patient, comprising: - movement means (11, 12, 12a, 13, 14, 16), implantable in the patient, for moving and displacing the cerebrospinal fluid in the cranial site of the patient in order to control the value of the actual intracranial pressure of said cerebrospinal fluid in said cranial site; - measuring means for measuring said intracranial pressure and providing data indicative ( PMIS) of its actual value, and - electronic monitoring and control means (20, 21, 22) for controlling the operation of said device; said implantable device being characterized in that said movement means, implantable in the patient, in turn comprise an assembly consisting of: - a micropump; - an intraventricular catheter connected at one end to said micropump; - a bag, made of yielding material, associated with the other end of catheter, said bag being designed to be inserted into a cerebral ventricle of the patient; and - an accumulation tank connected to said micropump; wherein said micropump, said catheter and said bag are filled with a certain volume of a service fluid which remains constant over time, and wherein said micropump is designed to extract said service fluid from said accumulation tank to supply said bag with said fluid, so as to dilate said bag in the ventricle, and to extract said service fluid from said bag to supply said accumulation tank with said fluid, so as to contract said bag in the ventricle, whereby the dilation/contraction of said bag causes a corresponding variation of the intracranial pressure of the cerebrospinal fluid in the cranial site of the patient; and in that said electronic monitoring and control means (20, 21, 22) are designed to process said data (Pmis) indicative of the intracranial pressure and to generate a corresponding control signal (S, V), in turn designed to drive said micropump and thereby to control the contraction and dilation of said bag in the cerebral ventricle, in such a way that the pattern of the intracranial pressure is maintained in time conforming to a desired pattern ( Pdes), and in particular the amplitude of the variable component of the intracranial pressure due to the cardiac cycle is minimized. - movement means (11, 12, 12a, 13, 14, 16), implantable in the patient, for moving and displacing the cerebrospinal fluid in the cranial site of the patient in order to control the value of the actual intracranial pressure of said cerebrospinal fluid in said cranial site; - measuring means for measuring said intracranial pressure and providing data indicative ( PMIS) of its actual value, and - electronic monitoring and control means (20, 21, 22) for controlling the operation of said device; said implantable device being characterized in that said movement means, implantable in the patient, in turn comprise an assembly consisting of: - a micropump; - an intraventricular catheter connected at one end to said micropump; - a bag, made of yielding material, associated with the other end of catheter, said bag being designed to be inserted into a cerebral ventricle of the patient; and - an accumulation tank connected to said micropump; wherein said micropump, said catheter and said bag are filled with a certain volume of a service fluid which remains constant over time, and wherein said micropump is designed to extract said service fluid from said accumulation tank to supply said bag with said fluid, so as to dilate said bag in the ventricle, and to extract said service fluid from said bag to supply said accumulation tank with said fluid, so as to contract said bag in the ventricle, whereby the dilation/contraction of said bag causes a corresponding variation of the intracranial pressure of the cerebrospinal fluid in the cranial site of the patient; and in that said electronic monitoring and control means (20, 21, 22) are designed to process said data (Pmis) indicative of the intracranial pressure and to generate a corresponding control signal (S, V), in turn designed to drive said micropump and thereby to control the contraction and dilation of said bag in the cerebral ventricle, in such a way that the pattern of the intracranial pressure is maintained in time conforming to a desired pattern ( Pdes), and in particular the amplitude of the variable component of the intracranial pressure due to the cardiac cycle is minimized.