Abstract: An implantable, passive bio-sensor (10) for monitoring internal physiological conditions of a patient is disclosed. The bio-sensor (10) includes at least one sensor or transducer (12) for monitoring a physiological condition of the patient and a passive transponder (14) that receives sensor signals from the sensor or sensors (12), digitizes the sensor signals, and transmits the digitized signals out of the patient's body when subjected to an externally generated interrogation signal. In one embodiment, the bio-sensor (100) is incorporated into the sidewall of a shunt (102) used for treating hydrocephalus for non-invasively monitoring the operation of the shunt (102).