In general, the disclosure relates to medical devices and systems configured to deliver posture-responsive therapy to a patient. For example, a medical system may detect a posture state of a patient and deliver therapy based at least in part on the detected patient posture state. In some examples, the system comprises a posture state sensor configured to generate first posture sensor data when a patient is in a first posture state. The system may further comprise a processor configured to define posture state reference data corresponding to the first posture state based at least in part on the first posture sensor data, and redefine the posture state reference data based on second posture data generated by the posture state sensor when the patient is in the first posture state.