Symmetry of loading during gait has been improved in individuals with amputations and joint replacements using an instrumented treadmill. However, this equipment is not readily available in clinics or at home where training typically occurs. Development of a cheaper, mobile system would allow for clinical adoption of these gait retraining techniques. PURPOSE: To determine the validity of calculating stance time asymmetry (STA) using a mobile application wirelessly connected to ankle-worn accelerometers. METHODS: A healthy male subject (35 yrs) walked on an instrumented treadmill for 30 seconds at 4 different speeds [1-1.6m/s] while varying between favoring his right side (RS), favoring his left side (LS), and normal (NL) walking. One 30 second trial of exclusive RS, LS, and NL walking were also collected at 1.2m/s. Accelerometers secured at both distal medial tibias streamed data via Bluetooth (approx. 500 Hz) to a mobile device. In real-time, a custom program on the mobile device calculated STA from the accelerometer data (AccelApp-based STA). Concurrently, treadmill force data (1500Hz) and foot markers were collected and used to calculate STA post-hoc (force-based STA). STA is the percent difference in stance time between successive right and left steps. RESULTS: 126 STAs were compared (Figure 1). STAs showed excellent agreement [Limits of Agreement (LOA): 1.3±5.3% (95% CI)] and were significantly correlated (r2=0.96, y=x+0.24%, p<0.0001 for intercept and slope). CONCLUSIONS: Based on this subject, STAs calculated with an ankle based accelerometer and mobile application system hold promise as a valid method to calculate STA. Additional subjects are currently being tested. Supported by BADER Consortium (DoD OR100017).