Techniques relate to operating a medical device in response to a detected posture state of a patient. A trigger event such as a request to modify how therapy is being delivered to the patient may cause a determination to be made as to whether the patient's posture state is stable. If the posture state is stable, an association is created between the posture state and one or more therapy parameter values. Over time, a library of such associations is created that may reflect any posture state in three dimensional space, wherein a posture state comprises at least one of a posture and an activity component. The library of associations may be used to automatically control therapy delivery. Similar ones of the associations may automatically be grouped into posture state regions to facilitate more efficient classification of the patient's posture state to control therapy delivery.
