This paper presents the design and development of an exergame for the wearable inertial sensor (WIS) system for performing range of motion (ROM) exercises. The salient features of the exergame include: (i) a sensor calibration user-interface (UI); (ii) a sensor mounting UI, (iii) a patient gaming UI; (iv) an instructor playback UI; and (v) an instructor exercise development UI. Along with the WIS system, the developed exergame UIs enable a user to perform ROM exercises in clinical and home-based environments. The exergame UIs can also be employed in a telerehabilitation setting for remote monitoring and assessment. Preliminary results on the efficacy of using the exergame environment is documented with: (i) sensor calibration time; (ii) sensor mounting and alignment time on the human body; and (iii) examination of user adherence to instructor programmed exercise routines.