An implantable device for controllably applying a neural stimulus, the device comprising: a plurality of electrodes including one or more stimulus electrodes (1, 2, 3) and one or more sense electrodes (6, 8); a stimulus source for providing a stimulus to be delivered from the one or more stimulus electrodes to a neural pathway of a patient in order to give rise to an evoked action potential on the neural pathway; measurement circuitry (128, 130) for recording a neural compound action potential signal sensed at the one or more sense electrodes; and a control unit configured to: control application of a neural stimulus as defined by a stimulus parameter; measure via the measurement circuitry (128, 130) a characteristic of a neural compound action potential response evoked by the stimulus; characterized in that the control unit is further configured to: compute, using the stimulus parameter and the measured characteristic of the evoked neural compound action potential response, a characteristic of an evoked response that would be obtained from the neural stimulus if the patient were in a reference posture; and estimate a posture of the patient from the computed characteristic. a plurality of electrodes including one or more stimulus electrodes (1, 2, 3) and one or more sense electrodes (6, 8); a stimulus source for providing a stimulus to be delivered from the one or more stimulus electrodes to a neural pathway of a patient in order to give rise to an evoked action potential on the neural pathway; measurement circuitry (128, 130) for recording a neural compound action potential signal sensed at the one or more sense electrodes; and a control unit configured to: control application of a neural stimulus as defined by a stimulus parameter; measure via the measurement circuitry (128, 130) a characteristic of a neural compound action potential response evoked by the stimulus; characterized in that the control unit is further configured to: compute, using the stimulus parameter and the measured characteristic of the evoked neural compound action potential response, a characteristic of an evoked response that would be obtained from the neural stimulus if the patient were in a reference posture; and estimate a posture of the patient from the computed characteristic. control application of a neural stimulus as defined by a stimulus parameter; measure via the measurement circuitry (128, 130) a characteristic of a neural compound action potential response evoked by the stimulus; characterized in that the control unit is further configured to: compute, using the stimulus parameter and the measured characteristic of the evoked neural compound action potential response, a characteristic of an evoked response that would be obtained from the neural stimulus if the patient were in a reference posture; and estimate a posture of the patient from the computed characteristic. compute, using the stimulus parameter and the measured characteristic of the evoked neural compound action potential response, a characteristic of an evoked response that would be obtained from the neural stimulus if the patient were in a reference posture; and estimate a posture of the patient from the computed characteristic.