An implantable medical device (IMD) is provided which is capable of sensing and determining its orientation, and of determining whether the IMD has been displaced over time away from its original or optimal position. Electronic components of the IMD, including a processor, digital memory, signal conditioning components, and a power supply, are preferably hermetically sealed within a biocompatible housing. At least three subcutaneous electrodes have fixed relative spacing for sensing electrical cardiac activity for various combinations of two electrodes, forming sensing vectors. Amplitude ratios and sign indicators associated with the sensing vectors are compared with a reference to determine an orientation of the device. In one embodiment, a telemetry unit transmits orientation data as a function of time to a remote device, and the remote device compares different stored orientations to detect displacement over time.