Systems and methods for monitoring cerebral spinal fluid (CSF) based on electrical impedance measurements are disclosed. The systems can include an excitation source of alternating current (202), at least two sensor electrodes (212,214) adapted for disposition within CSF in a ventricle of a subject's brain, and an impedance measuring device (204) electrically connected to the sensor electrodes (212,214) to measure impedance of CSF. Methods for controlling hydrocephalus are also disclosed and such methods can include the steps of disposing an impedance sensor (902) within CSF in a ventricle of a subject's brain, measuring impedance of the CSF with the sensor (902), and withdrawing CSF when the impedance measurement is less than a threshold value.