Abstract: Methods and systems for monitoring the condition of a septum in an implantable medical device are disclosed. Monitoring of the septum provides the ability to determine whether a needle has pierced the septum to effect the transfer of fluids into or out of a reservoir in the implantable medical device. Septum monitoring may provide the ability to determine whether the septum is maintaining its ability to seal the reservoir against leakage. The systems of the present invention include an ultrasonic transducer acoustically coupled to the septum to emit ultrasonic energy directly into the septum. Insertion of a needle through the septum can be detected by the acoustical changes caused by the needle located within the septum.