A housing for an implantable medical device comprises a metallic wall including a telemetry window having a thickness that is thinner than the remainder of the housing wall and having an electrical conductivity that is less than that of the remainder of the housing wall. In another embodiment, an implantable medical device casing comprises a metallic wall including a telemetry window received within an aperture defined by said casing wall, the window having an electrical conductivity that is less than that of the remainder of the casing wall. Pursuant to another embodiment, there is provided an implantable medical device incorporating a casing as described above that is hermetically sealed and encloses a transceiver for bidirectional telemetric communication through the telemetry window.